selinux/

security_server.rs

// Copyright 2023 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use crate::access_vector_cache::{
    AccessVectorCache, CacheStats, KernelXpermsAccessDecision, Query,
};
use crate::exceptions_config::ExceptionsConfig;
use crate::new_policy::HandleUnknown;
use crate::new_policy::traits::{HasName, HasPolicyId};
use crate::permission_check::{PerThreadCache, PermissionCheck};
use crate::policy::parser::PolicyData;
use crate::policy::{
    AccessDecision, AccessVector, AccessVectorComputer, ClassId, FsUseLabelAndType, FsUseType,
    KernelAccessDecision, PermissionId, Policy, SELINUX_AVD_FLAGS_PERMISSIVE, SecurityContext,
    XpermsBitmap, XpermsKind, parse_policy_by_value,
};
use crate::sid_table::SidTable;
use crate::sync::RwLock;
use crate::{
    ClassPermission, FileSystemLabel, FileSystemLabelingScheme, FileSystemMountOptions,
    FileSystemMountSids, FsNodeClass, InitialSid, KernelClass, KernelPermission, NullessByteStr,
    ObjectClass, PolicyCap, SeLinuxStatus, SeLinuxStatusPublisher, SecurityId,
};
use anyhow::Context as _;
use std::collections::HashMap;
use std::ops::DerefMut;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, AtomicU32, Ordering};

const ROOT_PATH: &'static str = "/";

struct ActivePolicy {
    /// Parsed policy structure.
    parsed: Arc<Policy>,

    /// Allocates and maintains the mapping between `SecurityId`s (SIDs) and Security Contexts.
    sid_table: SidTable,

    /// Describes access checks that should be granted, with associated bug Ids.
    exceptions: ExceptionsConfig,
}

#[derive(Default)]
struct SeLinuxBooleans {
    /// Active values for all of the booleans defined by the policy.
    /// Entries are created at policy load for each policy-defined conditional.
    active: HashMap<String, bool>,
    /// Pending values for any booleans modified since the last commit.
    pending: HashMap<String, bool>,
}

impl SeLinuxBooleans {
    fn reset(&mut self, booleans: Vec<(String, bool)>) {
        self.active = HashMap::from_iter(booleans);
        self.pending.clear();
    }
    fn names(&self) -> Vec<String> {
        self.active.keys().cloned().collect()
    }
    fn set_pending(&mut self, name: &str, value: bool) -> Result<(), ()> {
        if !self.active.contains_key(name) {
            return Err(());
        }
        self.pending.insert(name.into(), value);
        Ok(())
    }
    fn get(&self, name: &str) -> Result<(bool, bool), ()> {
        let active = self.active.get(name).ok_or(())?;
        let pending = self.pending.get(name).unwrap_or(active);
        Ok((*active, *pending))
    }
    fn commit_pending(&mut self) {
        self.active.extend(self.pending.drain());
    }
}

struct SecurityServerState {
    /// Describes the currently active policy.
    active_policy: Option<ActivePolicy>,

    /// Holds active and pending states for each boolean defined by policy.
    booleans: SeLinuxBooleans,

    /// Write-only interface to the data stored in the selinuxfs status file.
    status_publisher: Option<Box<dyn SeLinuxStatusPublisher>>,
}

impl SecurityServerState {
    fn deny_unknown(&self) -> bool {
        self.active_policy
            .as_ref()
            .map_or(true, |p| p.parsed.handle_unknown() != HandleUnknown::Allow)
    }
    fn reject_unknown(&self) -> bool {
        self.active_policy
            .as_ref()
            .map_or(false, |p| p.parsed.handle_unknown() == HandleUnknown::Reject)
    }

    fn expect_active_policy(&self) -> &ActivePolicy {
        &self.active_policy.as_ref().expect("policy should be loaded")
    }

    fn expect_active_policy_mut(&mut self) -> &mut ActivePolicy {
        self.active_policy.as_mut().expect("policy should be loaded")
    }

    fn compute_access_decision_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: ObjectClass,
    ) -> AccessDecision {
        let Some(active_policy) = self.active_policy.as_ref() else {
            // All permissions are allowed when no policy is loaded, regardless of enforcing state.
            return AccessDecision::allow(AccessVector::ALL);
        };

        let source_context = active_policy.sid_table.sid_to_security_context(source_sid);
        let target_context = active_policy.sid_table.sid_to_security_context(target_sid);

        let mut decision = active_policy.parsed.compute_access_decision(
            &source_context,
            &target_context,
            target_class,
        );

        decision.todo_bug = active_policy.exceptions.lookup(
            source_context.type_(),
            target_context.type_(),
            target_class,
        );

        decision
    }
}

pub(crate) struct SecurityServerBackend {
    /// The mutable state of the security server.
    state: RwLock<SecurityServerState>,

    /// True if the security server is enforcing, rather than permissive.
    /// Only modified with the `state` lock taken.
    is_enforcing: AtomicBool,

    /// Count of changes to the active policy.  Changes include both loads
    /// of complete new policies, and modifications to a previously loaded
    /// policy, e.g. by committing new values to conditional booleans in it.
    /// Only modified with the `state` lock taken.
    policy_change_count: AtomicU32,
}

/// An opaque identifier for the policy version, which can be used to detect if the policy has changed.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct PolicySeqNo(u32);

pub struct SecurityServer {
    /// The access vector cache that is shared between threads subject to access control by this
    /// security server.
    access_vector_cache: AccessVectorCache,

    /// A shared reference to the security server's state.
    backend: Arc<SecurityServerBackend>,

    /// Optional set of exceptions to apply to access checks, via `ExceptionsConfig`.
    exceptions: Vec<String>,
}

impl SecurityServer {
    /// Returns an instance with default configuration and no exceptions.
    pub fn new_default() -> Arc<Self> {
        Self::new(String::new(), Vec::new())
    }

    /// Returns an instance with the specified options and exceptions configured.
    pub fn new(options: String, exceptions: Vec<String>) -> Arc<Self> {
        // No options are currently supported.
        assert_eq!(options, String::new());

        let backend = Arc::new(SecurityServerBackend {
            state: RwLock::new(SecurityServerState {
                active_policy: None,
                booleans: SeLinuxBooleans::default(),
                status_publisher: None,
            }),
            is_enforcing: AtomicBool::new(false),
            policy_change_count: AtomicU32::new(0),
        });

        let access_vector_cache = AccessVectorCache::new(backend.clone());

        Arc::new(Self { access_vector_cache, backend, exceptions })
    }

    /// Converts a shared pointer to [`SecurityServer`] to a [`PermissionCheck`] without consuming
    /// the pointer.
    pub fn as_permission_check<'a>(
        self: &'a Self,
        local_cache: &'a PerThreadCache,
    ) -> PermissionCheck<'a> {
        PermissionCheck::new(self, &self.access_vector_cache, local_cache)
    }

    /// Returns the security ID mapped to `security_context`, creating it if it does not exist.
    ///
    /// All objects with the same security context will have the same SID associated.
    pub fn security_context_to_sid(
        &self,
        security_context: NullessByteStr<'_>,
    ) -> Result<SecurityId, anyhow::Error> {
        self.backend.compute_sid(|active_policy| {
            active_policy
                .parsed
                .parse_security_context(security_context)
                .map_err(anyhow::Error::from)
        })
    }

    /// Returns the Security Context string for the requested `sid`.
    /// This is used only where Contexts need to be stringified to expose to userspace, as
    /// is the case for e.g. the `/proc/*/attr/` filesystem and `security.selinux` extended
    /// attribute values.
    pub fn sid_to_security_context(&self, sid: SecurityId) -> Option<Vec<u8>> {
        let locked_state = self.backend.state.read();
        let active_policy = locked_state.active_policy.as_ref()?;
        let context = active_policy.sid_table.try_sid_to_security_context(sid)?;
        Some(active_policy.parsed.serialize_security_context(context))
    }

    /// Returns the Security Context for the requested `sid` with a terminating NUL.
    pub fn sid_to_security_context_with_nul(&self, sid: SecurityId) -> Option<Vec<u8>> {
        self.sid_to_security_context(sid).map(|mut context| {
            context.push(0u8);
            context
        })
    }

    /// Applies the supplied policy to the security server.
    pub fn load_policy(&self, binary_policy: Vec<u8>) -> Result<(), anyhow::Error> {
        // Parse the supplied policy, and reject the load operation if it is
        // malformed or invalid.
        let unvalidated_policy = parse_policy_by_value(binary_policy)?;
        let parsed = Arc::new(unvalidated_policy.validate()?);

        let exceptions = self.exceptions.iter().map(String::as_str).collect::<Vec<&str>>();
        let exceptions = ExceptionsConfig::new(&parsed, &exceptions)?;

        // Replace any existing policy and push update to `state.status_publisher`.
        self.with_mut_state_and_update_status(|state| {
            let sid_table = if let Some(previous_active_policy) = &state.active_policy {
                SidTable::new_from_previous(parsed.clone(), &previous_active_policy.sid_table)
            } else {
                SidTable::new(parsed.clone())
            };

            // TODO(b/324265752): Determine whether SELinux booleans need to be retained across
            // policy (re)loads.
            state.booleans.reset(
                parsed
                    .conditional_booleans()
                    .iter()
                    // TODO(b/324392507): Relax the UTF8 requirement on policy strings.
                    .map(|(name, value)| (String::from_utf8((*name).to_vec()).unwrap(), *value))
                    .collect(),
            );

            state.active_policy = Some(ActivePolicy { parsed, sid_table, exceptions });
            self.backend.policy_change_count.fetch_add(1, Ordering::Relaxed);
        });

        Ok(())
    }

    /// Returns true if a policy has been loaded.
    pub fn has_policy(&self) -> bool {
        self.backend.state.read().active_policy.is_some()
    }

    /// Returns the active policy in binary form, or `None` if no policy has yet been loaded.
    pub fn get_binary_policy(&self) -> Option<PolicyData> {
        let state = self.backend.state.read();
        let active_policy = state.active_policy.as_ref()?;
        Some(active_policy.parsed.serialize())
    }

    /// Set to enforcing mode if `enforce` is true, permissive mode otherwise.
    pub fn set_enforcing(&self, enforcing: bool) {
        self.with_mut_state_and_update_status(|_| {
            self.backend.is_enforcing.store(enforcing, Ordering::Release);
        });
    }

    pub fn is_enforcing(&self) -> bool {
        self.backend.is_enforcing.load(Ordering::Acquire)
    }

    /// Returns true if the policy requires unknown class / permissions to be
    /// denied. Defaults to true until a policy is loaded.
    pub fn deny_unknown(&self) -> bool {
        self.backend.state.read().deny_unknown()
    }

    /// Returns true if the policy requires unknown class / permissions to be
    /// rejected. Defaults to false until a policy is loaded.
    pub fn reject_unknown(&self) -> bool {
        self.backend.state.read().reject_unknown()
    }

    /// Returns the list of names of boolean conditionals defined by the
    /// loaded policy.
    pub fn conditional_booleans(&self) -> Vec<String> {
        self.backend.state.read().booleans.names()
    }

    /// Returns the active and pending values of a policy boolean, if it exists.
    pub fn get_boolean(&self, name: &str) -> Result<(bool, bool), ()> {
        self.backend.state.read().booleans.get(name)
    }

    /// Sets the pending value of a boolean, if it is defined in the policy.
    pub fn set_pending_boolean(&self, name: &str, value: bool) -> Result<(), ()> {
        self.backend.state.write().booleans.set_pending(name, value)
    }

    /// Commits all pending changes to conditional booleans.
    pub fn commit_pending_booleans(&self) {
        // TODO(b/324264149): Commit values into the stored policy itself.
        self.with_mut_state_and_update_status(|state| {
            state.booleans.commit_pending();
            self.backend.policy_change_count.fetch_add(1, Ordering::Relaxed);
        });
    }

    /// Returns whether a standard policy capability is enabled in the loaded policy.
    pub fn is_policycap_enabled(&self, policy_cap: PolicyCap) -> bool {
        let locked_state = self.backend.state.read();
        let Some(policy) = &locked_state.active_policy else {
            return false;
        };
        policy.parsed.has_policycap(policy_cap)
    }

    /// Returns a snapshot of the AVC usage statistics.
    pub fn avc_cache_stats(&self) -> CacheStats {
        self.access_vector_cache.cache_stats()
    }

    /// Returns the current policy version.
    pub fn policy_seqno(&self) -> PolicySeqNo {
        PolicySeqNo(self.backend.policy_change_count.load(Ordering::Relaxed))
    }

    /// Returns the list of all class names.
    pub fn class_names(&self) -> Result<Vec<Vec<u8>>, ()> {
        let locked_state = self.backend.state.read();
        let names = locked_state
            .expect_active_policy()
            .parsed
            .classes()
            .iter()
            .map(|class| class.name().to_vec())
            .collect();
        Ok(names)
    }

    /// Returns the class identifier of a class, if it exists.
    pub fn class_id_by_name(&self, name: &str) -> Result<ClassId, ()> {
        let locked_state = self.backend.state.read();
        Ok(locked_state
            .expect_active_policy()
            .parsed
            .classes()
            .get_by_name(name.as_bytes())
            .ok_or(())?
            .id())
    }

    /// Returns the set of permissions associated with a class. Each permission
    /// is represented as a tuple of the permission ID (in the scope of its
    /// associated class) and the permission name.
    pub fn class_permissions_by_name(
        &self,
        name: &str,
    ) -> Result<Vec<(PermissionId, Vec<u8>)>, ()> {
        let locked_state = self.backend.state.read();
        locked_state.expect_active_policy().parsed.find_class_permissions_by_name(name)
    }

    /// Determines the appropriate [`FileSystemLabel`] for a mounted filesystem given this security
    /// server's loaded policy, the name of the filesystem type ("ext4" or "tmpfs", for example),
    /// and the security-relevant mount options passed for the mount operation.
    pub fn resolve_fs_label(
        &self,
        fs_type: NullessByteStr<'_>,
        mount_options: &FileSystemMountOptions,
    ) -> Result<FileSystemLabel, anyhow::Error> {
        let mut locked_state = self.backend.state.write();
        let active_policy = locked_state.expect_active_policy_mut();

        let mount_sids = FileSystemMountSids {
            context: sid_from_mount_option(active_policy, &mount_options.context)?,
            fs_context: sid_from_mount_option(active_policy, &mount_options.fs_context)?,
            def_context: sid_from_mount_option(active_policy, &mount_options.def_context)?,
            root_context: sid_from_mount_option(active_policy, &mount_options.root_context)?,
        };
        let label = if let Some(mountpoint_sid) = mount_sids.context {
            // `mount_options` has `context` set, so the file-system and the nodes it contains are
            // labeled with that value, which is not modifiable. The `fs_context` option, if set,
            // overrides the file-system label.
            FileSystemLabel {
                sid: mount_sids.fs_context.unwrap_or(mountpoint_sid),
                scheme: FileSystemLabelingScheme::Mountpoint { sid: mountpoint_sid },
                mount_sids,
            }
        } else if let Some(FsUseLabelAndType { context, use_type }) =
            active_policy.parsed.fs_use_label_and_type(fs_type)
        {
            // There is an `fs_use` statement for this file-system type in the policy.
            let fs_sid_from_policy =
                active_policy.sid_table.security_context_to_sid(&context).unwrap();
            let fs_sid = mount_sids.fs_context.unwrap_or(fs_sid_from_policy);
            FileSystemLabel {
                sid: fs_sid,
                scheme: FileSystemLabelingScheme::FsUse {
                    fs_use_type: use_type,
                    default_sid: mount_sids.def_context.unwrap_or_else(|| InitialSid::File.into()),
                },
                mount_sids,
            }
        } else if let Some(context) =
            active_policy.parsed.genfscon_label_for_fs_and_path(fs_type, ROOT_PATH.into(), None)
        {
            // There is a `genfscon` statement for this file-system type in the policy.
            let genfscon_sid = active_policy.sid_table.security_context_to_sid(&context).unwrap();
            let fs_sid = mount_sids.fs_context.unwrap_or(genfscon_sid);

            // For relabeling to make sense with `genfscon` labeling they must ensure to persist the
            // `FsNode` security state. That is implicitly the case for filesystems which persist all
            // `FsNode`s in-memory (independent of the `DirEntry` cache), e.g. those whose contents are
            // managed as a `SimpleDirectory` structure.
            //
            // TODO: https://fxbug.dev/362898792 - Replace this with a more graceful mechanism for
            // deciding whether `genfscon` supports relabeling (as indicated by the "seclabel" tag
            // reported by `mount`).
            // Also consider storing the "genfs_seclabel_symlinks" setting in the resolved label.
            let fs_type = fs_type.as_bytes();
            let mut supports_seclabel = matches!(fs_type, b"sysfs" | b"tracefs" | b"pstore");
            supports_seclabel |= matches!(fs_type, b"cgroup" | b"cgroup2")
                && active_policy.parsed.has_policycap(PolicyCap::CgroupSeclabel);
            supports_seclabel |= fs_type == b"functionfs"
                && active_policy.parsed.has_policycap(PolicyCap::FunctionfsSeclabel);

            FileSystemLabel {
                sid: fs_sid,
                scheme: FileSystemLabelingScheme::GenFsCon { supports_seclabel },
                mount_sids,
            }
        } else {
            // The name of the filesystem type was not recognized.
            FileSystemLabel {
                sid: mount_sids.fs_context.unwrap_or_else(|| InitialSid::Unlabeled.into()),
                scheme: FileSystemLabelingScheme::FsUse {
                    fs_use_type: FsUseType::Xattr,
                    default_sid: mount_sids.def_context.unwrap_or_else(|| InitialSid::File.into()),
                },
                mount_sids,
            }
        };
        Ok(label)
    }

    /// Returns the [`SecurityId`] with which to label an [`FsNode`] in a filesystem of `fs_type`,
    /// at the specified filesystem-relative `node_path`.  Callers are responsible for ensuring that
    /// this API is never called prior to a policy first being loaded, or for a filesystem that is
    /// not configured to be `genfscon`-labeled.
    pub fn genfscon_label_for_fs_and_path(
        &self,
        fs_type: NullessByteStr<'_>,
        node_path: NullessByteStr<'_>,
        class_id: Option<KernelClass>,
    ) -> Result<SecurityId, anyhow::Error> {
        self.backend.compute_sid(|active_policy| {
            active_policy
                .parsed
                .genfscon_label_for_fs_and_path(fs_type, node_path.into(), class_id)
                .ok_or_else(|| {
                    anyhow::anyhow!("Genfscon label requested for non-genfscon labeled filesystem")
                })
        })
    }

    /// Returns true if the `bounded_sid` is bounded by the `parent_sid`.
    /// Bounds relationships are mostly enforced by policy tooling, so this only requires validating
    /// that the policy entry for the `TypeId` of `bounded_sid` has the `TypeId` of `parent_sid`
    /// specified in its `bounds`.
    pub fn is_bounded_by(&self, bounded_sid: SecurityId, parent_sid: SecurityId) -> bool {
        let locked_state = self.backend.state.read();
        let active_policy = locked_state.expect_active_policy();
        let bounded_type = active_policy.sid_table.sid_to_security_context(bounded_sid).type_();
        let parent_type = active_policy.sid_table.sid_to_security_context(parent_sid).type_();
        active_policy.parsed.is_bounded_by(bounded_type, parent_type)
    }

    /// Assign a [`SeLinuxStatusPublisher`] to be used for pushing updates to the security server's
    /// policy status. This should be invoked exactly once when `selinuxfs` is initialized.
    ///
    /// # Panics
    ///
    /// This will panic on debug builds if it is invoked multiple times.
    pub fn set_status_publisher(&self, status_holder: Box<dyn SeLinuxStatusPublisher>) {
        self.with_mut_state_and_update_status(|state| {
            assert!(state.status_publisher.is_none());
            state.status_publisher = Some(status_holder);
        });
    }

    /// Locks the security server state for modification and calls the supplied function to update
    /// it.  Once the update is complete, the configured `SeLinuxStatusPublisher` (if any) is called
    /// to update the userspace-facing "status" file to reflect the new state.
    fn with_mut_state_and_update_status(&self, f: impl FnOnce(&mut SecurityServerState)) {
        let mut locked_state = self.backend.state.write();
        f(locked_state.deref_mut());
        let new_value = SeLinuxStatus {
            is_enforcing: self.is_enforcing(),
            change_count: self.backend.policy_change_count.load(Ordering::Relaxed),
            deny_unknown: locked_state.deny_unknown(),
        };
        if let Some(status_publisher) = &mut locked_state.status_publisher {
            status_publisher.set_status(new_value);
        }

        // TODO: https://fxbug.dev/367585803 - reset the cache after running `f` and before updating
        // the userspace-facing "status", once that is possible.
        std::mem::drop(locked_state);
        self.access_vector_cache.reset();
    }

    /// Returns the security identifier (SID) with which to label a new object of `target_class`,
    /// based on the specified source & target security SIDs.
    /// For file-like classes the `compute_new_fs_node_sid*()` APIs should be used instead.
    // TODO: Move this API to sit alongside the other `compute_*()` APIs.
    // TODO: https://fxbug.dev/335397745 - APIs should not mix SecurityId and (raw) ClassId.
    pub fn compute_create_sid_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: ClassId,
    ) -> Result<SecurityId, anyhow::Error> {
        self.backend.compute_create_sid_raw(source_sid, target_sid, target_class.into())
    }

    /// Returns the security identifier ([`SecurityId`]) with which to label a new filesystem node of
    /// [`FsNodeClass`] with the given name, based on the specified source and target security SIDs.
    /// Evaluates filename transition rules uncached, falling back to default create SID computation
    /// if no filename transition rule matches.
    pub fn compute_new_fs_node_sid_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        fs_node_class: FsNodeClass,
        fs_node_name: NullessByteStr<'_>,
    ) -> Result<SecurityId, anyhow::Error> {
        self.backend.compute_new_fs_node_sid_raw(
            source_sid,
            target_sid,
            fs_node_class,
            fs_node_name,
        )
    }

    /// Returns the raw `AccessDecision` for a specified source, target and class.
    // TODO: APIs should not mix SecurityId and (raw) ClassId.
    pub fn compute_access_decision_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: ClassId,
    ) -> AccessDecision {
        self.backend.compute_access_decision_raw(source_sid, target_sid, target_class.into())
    }
}

impl SecurityServerBackend {
    fn compute_create_sid_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: ObjectClass,
    ) -> Result<SecurityId, anyhow::Error> {
        self.compute_sid(|active_policy| {
            let source_context = active_policy.sid_table.sid_to_security_context(source_sid);
            let target_context = active_policy.sid_table.sid_to_security_context(target_sid);

            Ok(active_policy.parsed.compute_create_context(
                source_context,
                target_context,
                target_class,
            ))
        })
        .context("computing new security context from policy")
    }

    fn compute_new_fs_node_sid_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        fs_node_class: FsNodeClass,
        fs_node_name: NullessByteStr<'_>,
    ) -> Result<SecurityId, anyhow::Error> {
        if !fs_node_name.as_bytes().is_empty() {
            if let Some(sid) = self.compute_new_fs_node_sid_with_name(
                source_sid,
                target_sid,
                fs_node_class,
                fs_node_name,
            ) {
                return Ok(sid);
            }
        }
        self.compute_create_sid_raw(source_sid, target_sid, fs_node_class.into())
    }

    /// Helper for call-sites that need to compute a `SecurityContext` and assign a SID to it.
    fn compute_sid(
        &self,
        compute_context: impl Fn(&ActivePolicy) -> Result<SecurityContext, anyhow::Error>,
    ) -> Result<SecurityId, anyhow::Error> {
        // Initially assume that the computed context will most likely already have a SID assigned,
        // so that the operation can be completed without any modification of the SID table.
        let readable_state = self.state.read();
        let policy_change_count = self.policy_change_count.load(Ordering::Relaxed);
        let policy_state = readable_state
            .active_policy
            .as_ref()
            .ok_or_else(|| anyhow::anyhow!("no policy loaded"))?;
        let context = compute_context(policy_state)?;
        if let Some(sid) = policy_state.sid_table.security_context_to_existing_sid(&context) {
            return Ok(sid);
        }
        std::mem::drop(readable_state);

        // Since the computed context was not found in the table, re-try the operation with the
        // policy state write-locked to allow for the SID table to be updated. In the rare case of
        // a new policy having been loaded in-between the read- and write-locked stages, the
        // `context` is re-computed using the new policy state.
        let mut writable_state = self.state.write();
        let needs_recompute =
            policy_change_count != self.policy_change_count.load(Ordering::Relaxed);
        let policy_state = writable_state.active_policy.as_mut().unwrap();
        let context = if needs_recompute { compute_context(policy_state)? } else { context };
        policy_state.sid_table.security_context_to_sid(&context).map_err(anyhow::Error::from)
    }

    fn compute_access_decision_raw(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: ObjectClass,
    ) -> AccessDecision {
        let locked_state = self.state.read();

        locked_state.compute_access_decision_raw(source_sid, target_sid, target_class)
    }
}

impl Query for SecurityServerBackend {
    fn compute_access_decision(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: KernelClass,
    ) -> KernelAccessDecision {
        let locked_state = self.state.read();
        let decision =
            locked_state.compute_access_decision_raw(source_sid, target_sid, target_class.into());
        locked_state.access_decision_to_kernel_access_decision(target_class, decision)
    }

    fn compute_create_sid(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        target_class: KernelClass,
    ) -> Result<SecurityId, anyhow::Error> {
        self.compute_create_sid_raw(source_sid, target_sid, target_class.into())
    }

    fn compute_new_fs_node_sid_with_name(
        &self,
        source_sid: SecurityId,
        target_sid: SecurityId,
        fs_node_class: FsNodeClass,
        fs_node_name: NullessByteStr<'_>,
    ) -> Option<SecurityId> {
        let mut locked_state = self.state.write();

        // This interface will not be reached without a policy having been loaded.
        let active_policy = locked_state.active_policy.as_mut().expect("Policy loaded");

        let source_context = active_policy.sid_table.sid_to_security_context(source_sid);
        let target_context = active_policy.sid_table.sid_to_security_context(target_sid);

        let new_file_context = active_policy.parsed.compute_create_context_with_name(
            source_context,
            target_context,
            fs_node_class,
            fs_node_name,
        )?;

        active_policy.sid_table.security_context_to_sid(&new_file_context).ok()
    }

    fn compute_xperms_access_decision(
        &self,
        xperms_kind: XpermsKind,
        source_sid: SecurityId,
        target_sid: SecurityId,
        permission: KernelPermission,
        xperms_prefix: u8,
    ) -> KernelXpermsAccessDecision {
        let locked_state = self.state.read();

        let active_policy = match &locked_state.active_policy {
            Some(active_policy) => active_policy,
            // All permissions are allowed when no policy is loaded, regardless of enforcing state.
            None => {
                return KernelXpermsAccessDecision {
                    allow: XpermsBitmap::ALL,
                    audit: XpermsBitmap::NONE,
                    permissive: false,
                    has_todo: false,
                };
            }
        };

        // Look up the decision for the base permission.
        // TODO(b/493591579): avoid multiple lookups in the SID table
        let base_decision_raw = locked_state.compute_access_decision_raw(
            source_sid,
            target_sid,
            permission.class().into(),
        );
        let base_decision = locked_state
            .access_decision_to_kernel_access_decision(permission.class(), base_decision_raw);
        let permission_access_vector = permission.as_access_vector();
        let base_permit =
            base_decision.allow & permission_access_vector == permission_access_vector;
        let base_audit = base_decision.audit & permission_access_vector == permission_access_vector;

        // Look up the extended permission decision.
        let source_context = active_policy.sid_table.sid_to_security_context(source_sid);
        let target_context = active_policy.sid_table.sid_to_security_context(target_sid);
        let xperms_decision = active_policy.parsed.compute_xperms_access_decision(
            xperms_kind,
            &source_context,
            &target_context,
            permission.class(),
            xperms_prefix,
        );

        // Combine the base and extended decisions.
        let allow = if !base_permit { XpermsBitmap::NONE } else { xperms_decision.allow };
        let audit = if base_audit {
            XpermsBitmap::ALL
        } else {
            (xperms_decision.allow & xperms_decision.auditallow)
                | (!xperms_decision.allow & xperms_decision.auditdeny)
        };
        let permissive = (base_decision.flags & SELINUX_AVD_FLAGS_PERMISSIVE) != 0;
        let has_todo = base_decision.todo_bug.is_some();
        KernelXpermsAccessDecision { allow, audit, permissive, has_todo }
    }
}

impl AccessVectorComputer for SecurityServerBackend {
    fn access_decision_to_kernel_access_decision(
        &self,
        class: KernelClass,
        av: AccessDecision,
    ) -> KernelAccessDecision {
        self.state.read().access_decision_to_kernel_access_decision(class, av)
    }
}

impl AccessVectorComputer for SecurityServerState {
    fn access_decision_to_kernel_access_decision(
        &self,
        class: KernelClass,
        av: AccessDecision,
    ) -> KernelAccessDecision {
        match &self.active_policy {
            Some(policy) => policy.parsed.access_decision_to_kernel_access_decision(class, av),
            None => KernelAccessDecision {
                allow: AccessVector::ALL,
                audit: AccessVector::NONE,
                flags: 0,
                todo_bug: None,
            },
        }
    }
}

/// Computes a [`SecurityId`] given a non-[`None`] value for one of the four
/// "context" mount options (https://man7.org/linux/man-pages/man8/mount.8.html).
fn sid_from_mount_option(
    active_policy: &mut ActivePolicy,
    mount_option: &Option<Vec<u8>>,
) -> Result<Option<SecurityId>, anyhow::Error> {
    let Some(label) = mount_option else {
        return Ok(None);
    };
    let context = active_policy.parsed.parse_security_context(label.into())?;
    let sid = active_policy.sid_table.security_context_to_sid(&context)?;
    Ok(Some(sid))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::permission_check::PermissionCheckResult;
    use crate::{
        CommonFsNodePermission, DirPermission, FileClass, FilePermission, ForClass, KernelClass,
        ProcessPermission,
    };
    use std::num::NonZeroU32;

    const TESTSUITE_BINARY_POLICY: &[u8] = include_bytes!("../testdata/policies/selinux_testsuite");
    const TESTS_BINARY_POLICY: &[u8] =
        include_bytes!("../testdata/micro_policies/security_server_tests_policy");
    const MINIMAL_BINARY_POLICY: &[u8] =
        include_bytes!("../testdata/composite_policies/compiled/minimal_policy");

    fn security_server_with_tests_policy() -> Arc<SecurityServer> {
        let policy_bytes = TESTS_BINARY_POLICY.to_vec();
        let security_server = SecurityServer::new_default();
        assert_eq!(
            Ok(()),
            security_server.load_policy(policy_bytes).map_err(|e| format!("{:?}", e))
        );
        security_server
    }

    #[test]
    fn compute_access_vector_allows_all() {
        let security_server = SecurityServer::new_default();
        let sid1 = InitialSid::Kernel.into();
        let sid2 = InitialSid::Unlabeled.into();
        assert_eq!(
            security_server
                .backend
                .compute_access_decision(sid1, sid2, KernelClass::Process.into())
                .allow,
            AccessVector::ALL
        );
    }

    #[test]
    fn loaded_policy_can_be_retrieved() {
        let security_server = security_server_with_tests_policy();
        assert_eq!(TESTS_BINARY_POLICY, security_server.get_binary_policy().unwrap().as_ref());
    }

    #[test]
    fn loaded_policy_is_validated() {
        let not_really_a_policy = "not a real policy".as_bytes().to_vec();
        let security_server = SecurityServer::new_default();
        assert!(security_server.load_policy(not_really_a_policy.clone()).is_err());
    }

    #[test]
    fn enforcing_mode_is_reported() {
        let security_server = SecurityServer::new_default();
        assert!(!security_server.is_enforcing());

        security_server.set_enforcing(true);
        assert!(security_server.is_enforcing());
    }

    #[test]
    fn without_policy_conditional_booleans_are_empty() {
        let security_server = SecurityServer::new_default();
        assert!(security_server.conditional_booleans().is_empty());
    }

    #[test]
    fn conditional_booleans_can_be_queried() {
        let policy_bytes = TESTSUITE_BINARY_POLICY.to_vec();
        let security_server = SecurityServer::new_default();
        assert_eq!(
            Ok(()),
            security_server.load_policy(policy_bytes).map_err(|e| format!("{:?}", e))
        );

        let booleans = security_server.conditional_booleans();
        assert!(!booleans.is_empty());
        let boolean = booleans[0].as_str();

        assert!(security_server.get_boolean("this_is_not_a_valid_boolean_name").is_err());
        assert!(security_server.get_boolean(boolean).is_ok());
    }

    #[test]
    fn conditional_booleans_can_be_changed() {
        let policy_bytes = TESTSUITE_BINARY_POLICY.to_vec();
        let security_server = SecurityServer::new_default();
        assert_eq!(
            Ok(()),
            security_server.load_policy(policy_bytes).map_err(|e| format!("{:?}", e))
        );

        let booleans = security_server.conditional_booleans();
        assert!(!booleans.is_empty());
        let boolean = booleans[0].as_str();

        let (active, pending) = security_server.get_boolean(boolean).unwrap();
        assert_eq!(active, pending, "Initially active and pending values should match");

        security_server.set_pending_boolean(boolean, !active).unwrap();
        let (active, pending) = security_server.get_boolean(boolean).unwrap();
        assert!(active != pending, "Before commit pending should differ from active");

        security_server.commit_pending_booleans();
        let (final_active, final_pending) = security_server.get_boolean(boolean).unwrap();
        assert_eq!(final_active, pending, "Pending value should be active after commit");
        assert_eq!(final_active, final_pending, "Active and pending are the same after commit");
    }

    #[test]
    fn parse_security_context_no_policy() {
        let security_server = SecurityServer::new_default();
        let error = security_server
            .security_context_to_sid(b"unconfined_u:unconfined_r:unconfined_t:s0".into())
            .expect_err("expected error");
        let error_string = format!("{:?}", error);
        assert!(error_string.contains("no policy"));
    }

    #[test]
    fn compute_new_fs_node_sid_no_defaults() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_no_defaults_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s1".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User and low security level should be copied from the source,
        // and the role and type from the target.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s0");
    }

    #[test]
    fn compute_new_fs_node_sid_source_defaults() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_source_defaults_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s2:c0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s1-s3:c0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // All fields should be copied from the source, but only the "low" part of the security
        // range.
        assert_eq!(computed_context, b"user_u:unconfined_r:unconfined_t:s0");
    }

    #[test]
    fn compute_new_fs_node_sid_target_defaults() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_target_defaults_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s2:c0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s1-s3:c0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User, role and type copied from target, with source's low security level.
        assert_eq!(computed_context, b"file_u:object_r:file_t:s0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_source_low_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_source_low_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s1".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User and low security level copied from source, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_source_low_high_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_source_low_high_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s1".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User and full security range copied from source, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s0-s1:c0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_source_high_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_source_high_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User and high security level copied from source, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s1:c0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_target_low_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_target_low_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s1".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User copied from source, low security level from target, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_target_low_high_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_target_low_high_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s1".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User copied from source, full security range from target, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s0-s1:c0");
    }

    #[test]
    fn compute_new_fs_node_sid_range_target_high_default() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/micro_policies/file_range_target_high_policy").to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"user_u:unconfined_r:unconfined_t:s0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"file_u:object_r:file_t:s0-s1:c0".into())
            .expect("creating SID from security context should succeed");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(source_sid, target_sid, FileClass::File.into(), "".into())
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // User copied from source, high security level from target, role and type as default.
        assert_eq!(computed_context, b"user_u:object_r:file_t:s1:c0");
    }

    #[test]
    fn compute_new_fs_node_sid_with_name() {
        let security_server = SecurityServer::new_default();
        let policy_bytes =
            include_bytes!("../testdata/composite_policies/compiled/type_transition_policy")
                .to_vec();
        security_server.load_policy(policy_bytes).expect("binary policy loads");

        let source_sid = security_server
            .security_context_to_sid(b"source_u:source_r:source_t:s0".into())
            .expect("creating SID from security context should succeed");
        let target_sid = security_server
            .security_context_to_sid(b"target_u:object_r:target_t:s0".into())
            .expect("creating SID from security context should succeed");

        const SPECIAL_FILE_NAME: &[u8] = b"special_file";
        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(
                source_sid,
                target_sid,
                FileClass::File.into(),
                SPECIAL_FILE_NAME.into(),
            )
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // New domain should be derived from the filename-specific rule.
        assert_eq!(computed_context, b"source_u:object_r:special_transition_t:s0");

        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(
                source_sid,
                target_sid,
                FileClass::ChrFile.into(),
                SPECIAL_FILE_NAME.into(),
            )
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // New domain should be copied from the target, because the class does not match either the
        // filename-specific nor generic type transition rules.
        assert_eq!(computed_context, b"source_u:object_r:target_t:s0");

        const OTHER_FILE_NAME: &[u8] = b"other_file";
        let computed_sid = security_server
            .as_permission_check(&Default::default())
            .compute_new_fs_node_sid(
                source_sid,
                target_sid,
                FileClass::File.into(),
                OTHER_FILE_NAME.into(),
            )
            .expect("new sid computed");
        let computed_context = security_server
            .sid_to_security_context(computed_sid)
            .expect("computed sid associated with context");

        // New domain should be derived from the non-filename-specific rule, because the filename
        // does not match.
        assert_eq!(computed_context, b"source_u:object_r:transition_t:s0");
    }

    #[test]
    fn permissions_are_fresh_after_different_policy_load() {
        let minimal_bytes = MINIMAL_BINARY_POLICY.to_vec();
        let allow_fork_bytes =
            include_bytes!("../testdata/composite_policies/compiled/allow_fork_policy").to_vec();
        let context = b"source_u:object_r:source_t:s0:c0";

        let security_server = SecurityServer::new_default();
        security_server.set_enforcing(true);

        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Load the minimal policy and get a SID for the context.
        assert_eq!(
            Ok(()),
            security_server.load_policy(minimal_bytes).map_err(|e| format!("{:?}", e))
        );
        let sid = security_server.security_context_to_sid(context.into()).unwrap();

        // The minimal policy does not grant fork allowance.
        assert!(!permission_check.has_permission(sid, sid, ProcessPermission::Fork).granted);

        // Load a policy that does grant fork allowance.
        assert_eq!(
            Ok(()),
            security_server.load_policy(allow_fork_bytes).map_err(|e| format!("{:?}", e))
        );

        // Reuse the cache to check invalidation.
        let permission_check = security_server.as_permission_check(&local_cache);

        // The now-loaded "allow_fork" policy allows the context represented by `sid` to fork.
        assert!(permission_check.has_permission(sid, sid, ProcessPermission::Fork).granted);
    }

    #[test]
    fn unknown_sids_are_effectively_unlabeled() {
        let with_unlabeled_access_domain_policy_bytes = include_bytes!(
            "../testdata/composite_policies/compiled/with_unlabeled_access_domain_policy"
        )
        .to_vec();
        let with_additional_domain_policy_bytes =
            include_bytes!("../testdata/composite_policies/compiled/with_additional_domain_policy")
                .to_vec();
        let allowed_type_context = b"source_u:object_r:allowed_t:s0:c0";
        let additional_type_context = b"source_u:object_r:additional_t:s0:c0";

        let security_server = SecurityServer::new_default();
        security_server.set_enforcing(true);

        // Load a policy, get a SID for a context that is valid for that policy, and verify
        // that a context that is not valid for that policy is not issued a SID.
        assert_eq!(
            Ok(()),
            security_server
                .load_policy(with_unlabeled_access_domain_policy_bytes.clone())
                .map_err(|e| format!("{:?}", e))
        );
        let allowed_type_sid =
            security_server.security_context_to_sid(allowed_type_context.into()).unwrap();
        assert!(security_server.security_context_to_sid(additional_type_context.into()).is_err());

        // Load the policy that makes the second context valid, and verify that it is valid, and
        // verify that the first context remains valid (and unchanged).
        assert_eq!(
            Ok(()),
            security_server
                .load_policy(with_additional_domain_policy_bytes.clone())
                .map_err(|e| format!("{:?}", e))
        );
        let additional_type_sid =
            security_server.security_context_to_sid(additional_type_context.into()).unwrap();
        assert_eq!(
            allowed_type_sid,
            security_server.security_context_to_sid(allowed_type_context.into()).unwrap()
        );

        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // "allowed_t" is allowed the process getsched capability to "unlabeled_t" - but since
        // the currently-loaded policy defines "additional_t", the SID for "additional_t" does
        // not get treated as effectively unlabeled, and these permission checks are denied.
        assert!(
            !permission_check
                .has_permission(additional_type_sid, allowed_type_sid, ProcessPermission::GetSched)
                .granted
        );
        assert!(
            !permission_check
                .has_permission(additional_type_sid, allowed_type_sid, ProcessPermission::SetSched)
                .granted
        );
        assert!(
            !permission_check
                .has_permission(allowed_type_sid, additional_type_sid, ProcessPermission::GetSched)
                .granted
        );
        assert!(
            !permission_check
                .has_permission(allowed_type_sid, additional_type_sid, ProcessPermission::SetSched)
                .granted
        );

        // We now flip back to the policy that does not recognize "additional_t"...
        assert_eq!(
            Ok(()),
            security_server
                .load_policy(with_unlabeled_access_domain_policy_bytes)
                .map_err(|e| format!("{:?}", e))
        );

        // Reuse the cache to check invalidation.
        let permission_check = security_server.as_permission_check(&local_cache);

        // The now-loaded policy allows "allowed_t" the process getsched capability
        // to "unlabeled_t" and since the now-loaded policy does not recognize "additional_t",
        // "allowed_t" is now allowed the process getsched capability to "additional_t".
        assert!(
            permission_check
                .has_permission(allowed_type_sid, additional_type_sid, ProcessPermission::GetSched)
                .granted
        );
        assert!(
            !permission_check
                .has_permission(allowed_type_sid, additional_type_sid, ProcessPermission::SetSched)
                .granted
        );

        // ... and the now-loaded policy also allows "unlabeled_t" the process
        // setsched capability to "allowed_t" and since the now-loaded policy does not recognize
        // "additional_t", "unlabeled_t" is now allowed the process setsched capability to
        // "allowed_t".
        assert!(
            !permission_check
                .has_permission(additional_type_sid, allowed_type_sid, ProcessPermission::GetSched)
                .granted
        );
        assert!(
            permission_check
                .has_permission(additional_type_sid, allowed_type_sid, ProcessPermission::SetSched)
                .granted
        );

        // We also verify that we do not get a serialization for unrecognized "additional_t"...
        assert!(security_server.sid_to_security_context(additional_type_sid).is_none());

        // ... but if we flip forward to the policy that recognizes "additional_t", then we see
        // the serialization succeed and return the original context string.
        assert_eq!(
            Ok(()),
            security_server
                .load_policy(with_additional_domain_policy_bytes)
                .map_err(|e| format!("{:?}", e))
        );
        assert_eq!(
            additional_type_context.to_vec(),
            security_server.sid_to_security_context(additional_type_sid).unwrap()
        );
    }

    #[test]
    fn permission_check_permissive() {
        let security_server = security_server_with_tests_policy();
        security_server.set_enforcing(false);
        assert!(!security_server.is_enforcing());

        let sid =
            security_server.security_context_to_sid("user0:object_r:type0:s0".into()).unwrap();
        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Test policy grants "type0" the process-fork permission to itself.
        // Since the permission is granted by policy, the check will not be audit logged.
        assert_eq!(
            permission_check.has_permission(sid, sid, ProcessPermission::Fork),
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );

        // Test policy does not grant "type0" the process-getrlimit permission to itself, but
        // the security server is configured to be permissive. Because the permission was not
        // granted by the policy, the check will be audit logged.
        let result = permission_check.has_permission(sid, sid, ProcessPermission::GetRlimit);
        assert_eq!(
            result,
            PermissionCheckResult { granted: false, audit: true, permissive: true, todo_bug: None }
        );
        assert!(result.permit());

        // Test policy is built with "deny unknown" behaviour, and has no "blk_file" class defined.
        // This permission should be treated like a defined permission that is not allowed to the
        // source, and both allowed and audited here.
        let result = permission_check.has_permission(
            sid,
            sid,
            CommonFsNodePermission::GetAttr.for_class(FileClass::BlkFile),
        );
        assert_eq!(
            result,
            PermissionCheckResult { granted: false, audit: true, permissive: true, todo_bug: None }
        );
        assert!(result.permit());
    }

    #[test]
    fn permission_check_enforcing() {
        let security_server = security_server_with_tests_policy();
        security_server.set_enforcing(true);
        assert!(security_server.is_enforcing());

        let sid =
            security_server.security_context_to_sid("user0:object_r:type0:s0".into()).unwrap();
        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Test policy grants "type0" the process-fork permission to itself.
        let result = permission_check.has_permission(sid, sid, ProcessPermission::Fork);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());

        // Test policy does not grant "type0" the process-getrlimit permission to itself.
        // Permission denials are audit logged in enforcing mode.
        let result = permission_check.has_permission(sid, sid, ProcessPermission::GetRlimit);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Test policy is built with "deny unknown" behaviour, and has no "blk_file" class defined.
        // This permission should therefore be denied, and the denial audited.
        let result = permission_check.has_permission(
            sid,
            sid,
            CommonFsNodePermission::GetAttr.for_class(FileClass::BlkFile),
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());
    }

    #[test]
    fn permissive_domain() {
        let security_server = security_server_with_tests_policy();
        security_server.set_enforcing(true);
        assert!(security_server.is_enforcing());

        let permissive_sid = security_server
            .security_context_to_sid("user0:object_r:permissive_t:s0".into())
            .unwrap();
        let non_permissive_sid = security_server
            .security_context_to_sid("user0:object_r:non_permissive_t:s0".into())
            .unwrap();

        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Test policy grants process-getsched permission to both of the test domains.
        let result = permission_check.has_permission(
            permissive_sid,
            permissive_sid,
            ProcessPermission::GetSched,
        );
        assert_eq!(
            result,
            PermissionCheckResult { granted: true, audit: false, permissive: true, todo_bug: None }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(
            non_permissive_sid,
            non_permissive_sid,
            ProcessPermission::GetSched,
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());

        // Test policy does not grant process-getsched permission to the test domains on one another.
        // The permissive domain will be granted the permission, since it is marked permissive.
        let result = permission_check.has_permission(
            permissive_sid,
            non_permissive_sid,
            ProcessPermission::GetSched,
        );
        assert_eq!(
            result,
            PermissionCheckResult { granted: false, audit: true, permissive: true, todo_bug: None }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(
            non_permissive_sid,
            permissive_sid,
            ProcessPermission::GetSched,
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Test policy has "deny unknown" behaviour and does not define the "blk_file" class, so
        // access to a permission on it will depend on whether the source is permissive.
        // The target domain is irrelevant, since the class/permission do not exist, so the non-
        // permissive SID is used for both checks.
        let result = permission_check.has_permission(
            permissive_sid,
            non_permissive_sid,
            CommonFsNodePermission::GetAttr.for_class(FileClass::BlkFile),
        );
        assert_eq!(
            result,
            PermissionCheckResult { granted: false, audit: true, permissive: true, todo_bug: None }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(
            non_permissive_sid,
            non_permissive_sid,
            CommonFsNodePermission::GetAttr.for_class(FileClass::BlkFile),
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());
    }

    #[test]
    fn auditallow_and_dontaudit() {
        let security_server = security_server_with_tests_policy();
        security_server.set_enforcing(true);
        assert!(security_server.is_enforcing());

        let audit_sid = security_server
            .security_context_to_sid("user0:object_r:test_audit_t:s0".into())
            .unwrap();

        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Test policy grants the domain self-fork permission, and marks it audit-allow.
        let result = permission_check.has_permission(audit_sid, audit_sid, ProcessPermission::Fork);
        assert_eq!(
            result,
            PermissionCheckResult { granted: true, audit: true, permissive: false, todo_bug: None }
        );
        assert!(result.permit());

        // Self-setsched permission is granted, and marked dont-audit, which takes no effect.
        let result =
            permission_check.has_permission(audit_sid, audit_sid, ProcessPermission::SetSched);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());

        // Self-getsched permission is denied, but marked dont-audit.
        let result =
            permission_check.has_permission(audit_sid, audit_sid, ProcessPermission::GetSched);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Self-getpgid permission is denied, with neither audit-allow nor dont-audit.
        let result =
            permission_check.has_permission(audit_sid, audit_sid, ProcessPermission::GetPgid);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());
    }

    #[test]
    fn access_checks_with_exceptions_config() {
        const EXCEPTIONS_CONFIG: &[&str] = &[
            // These statement should all be resolved.
            "todo_deny b/001 test_exception_source_t test_exception_target_t file",
            "todo_deny b/002 test_exception_other_t test_exception_target_t chr_file",
            "todo_deny b/003 test_exception_source_t test_exception_other_t anon_inode",
            "todo_deny b/004 test_exception_permissive_t test_exception_target_t file",
            "todo_permissive b/005 test_exception_todo_permissive_t",
            // These statements should not be resolved.
            "todo_deny b/101 test_undefined_source_t test_exception_target_t file",
            "todo_deny b/102 test_exception_source_t test_undefined_target_t file",
            "todo_permissive b/103 test_undefined_source_t",
        ];
        let exceptions_config = EXCEPTIONS_CONFIG.iter().map(|x| String::from(*x)).collect();
        let security_server = SecurityServer::new(String::new(), exceptions_config);
        security_server.set_enforcing(true);

        const EXCEPTIONS_POLICY: &[u8] =
            include_bytes!("../testdata/composite_policies/compiled/exceptions_config_policy");
        assert!(security_server.load_policy(EXCEPTIONS_POLICY.into()).is_ok());

        let source_sid = security_server
            .security_context_to_sid("test_exception_u:object_r:test_exception_source_t:s0".into())
            .unwrap();
        let target_sid = security_server
            .security_context_to_sid("test_exception_u:object_r:test_exception_target_t:s0".into())
            .unwrap();
        let other_sid = security_server
            .security_context_to_sid("test_exception_u:object_r:test_exception_other_t:s0".into())
            .unwrap();
        let permissive_sid = security_server
            .security_context_to_sid(
                "test_exception_u:object_r:test_exception_permissive_t:s0".into(),
            )
            .unwrap();
        let unmatched_sid = security_server
            .security_context_to_sid(
                "test_exception_u:object_r:test_exception_unmatched_t:s0".into(),
            )
            .unwrap();
        let todo_permissive_sid = security_server
            .security_context_to_sid(
                "test_exception_u:object_r:test_exception_todo_permissive_t:s0".into(),
            )
            .unwrap();

        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Source SID has no "process" permissions to target SID, and no exceptions.
        let result =
            permission_check.has_permission(source_sid, target_sid, ProcessPermission::GetPgid);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Source SID has no "file:entrypoint" permission to target SID, but there is an exception defined.
        let result =
            permission_check.has_permission(source_sid, target_sid, FilePermission::Entrypoint);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: false,
                todo_bug: Some(NonZeroU32::new(1).unwrap())
            }
        );
        assert!(result.permit());

        // Source SID has "file:execute_no_trans" permission to target SID.
        let result =
            permission_check.has_permission(source_sid, target_sid, FilePermission::ExecuteNoTrans);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None,
            }
        );
        assert!(result.permit());

        // Other SID has no "file:entrypoint" permissions to target SID, and the exception does not match "file" class.
        let result =
            permission_check.has_permission(other_sid, target_sid, FilePermission::Entrypoint);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Other SID has no "chr_file" permissions to target SID, but there is an exception defined.
        let result = permission_check.has_permission(
            other_sid,
            target_sid,
            CommonFsNodePermission::Read.for_class(FileClass::ChrFile),
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: false,
                todo_bug: Some(NonZeroU32::new(2).unwrap())
            }
        );
        assert!(result.permit());

        // Source SID has no "file:entrypoint" permissions to unmatched SID, and no exception is defined.
        let result =
            permission_check.has_permission(source_sid, unmatched_sid, FilePermission::Entrypoint);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Unmatched SID has no "file:entrypoint" permissions to target SID, and no exception is defined.
        let result =
            permission_check.has_permission(unmatched_sid, target_sid, FilePermission::Entrypoint);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Todo-deny exceptions are processed before the permissive bit is handled.
        let result =
            permission_check.has_permission(permissive_sid, target_sid, FilePermission::Entrypoint);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: true,
                todo_bug: Some(NonZeroU32::new(4).unwrap())
            }
        );
        assert!(result.permit());

        // Todo-permissive SID is not granted any permissions, so all permissions should be granted,
        // to all target domains and classes, and all grants should be associated with the bug.
        let result = permission_check.has_permission(
            todo_permissive_sid,
            target_sid,
            FilePermission::Entrypoint,
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: false,
                todo_bug: Some(NonZeroU32::new(5).unwrap())
            }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(
            todo_permissive_sid,
            todo_permissive_sid,
            FilePermission::Entrypoint,
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: false,
                todo_bug: Some(NonZeroU32::new(5).unwrap())
            }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(
            todo_permissive_sid,
            target_sid,
            FilePermission::Entrypoint,
        );
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: true,
                permissive: false,
                todo_bug: Some(NonZeroU32::new(5).unwrap())
            }
        );
        assert!(result.permit());
    }

    #[test]
    fn handle_unknown() {
        let security_server = security_server_with_tests_policy();

        let sid = security_server
            .security_context_to_sid("user0:object_r:type0:s0".into())
            .expect("Resolve Context to SID");

        // Load a policy that is missing some elements, and marked handle_unknown=reject.
        // The policy should be rejected, since not all classes/permissions are defined.
        // Rejecting policy is not controlled by permissive vs enforcing.
        const REJECT_POLICY: &[u8] =
            include_bytes!("../testdata/composite_policies/compiled/handle_unknown_policy-reject");
        assert!(security_server.load_policy(REJECT_POLICY.to_vec()).is_err());

        security_server.set_enforcing(true);

        // Load a policy that is missing some elements, and marked handle_unknown=deny.
        const DENY_POLICY: &[u8] =
            include_bytes!("../testdata/composite_policies/compiled/handle_unknown_policy-deny");
        assert!(security_server.load_policy(DENY_POLICY.to_vec()).is_ok());
        let local_cache = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache);

        // Check against undefined classes or permissions should deny access and audit.
        let result = permission_check.has_permission(sid, sid, ProcessPermission::GetSched);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());
        let result = permission_check.has_permission(sid, sid, DirPermission::AddName);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Check that permissions that are defined are unaffected by handle-unknown.
        let result = permission_check.has_permission(sid, sid, DirPermission::Search);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(sid, sid, DirPermission::Reparent);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());

        // Load a policy that is missing some elements, and marked handle_unknown=allow.
        const ALLOW_POLICY: &[u8] =
            include_bytes!("../testdata/composite_policies/compiled/handle_unknown_policy-allow");
        assert!(security_server.load_policy(ALLOW_POLICY.to_vec()).is_ok());
        let local_cache2 = Default::default();
        let permission_check = security_server.as_permission_check(&local_cache2);

        // Check against undefined classes or permissions should grant access without audit.
        let result = permission_check.has_permission(sid, sid, ProcessPermission::GetSched);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());
        let result = permission_check.has_permission(sid, sid, DirPermission::AddName);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());

        // Check that permissions that are defined are unaffected by handle-unknown.
        let result = permission_check.has_permission(sid, sid, DirPermission::Search);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: true,
                audit: false,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(result.permit());

        let result = permission_check.has_permission(sid, sid, DirPermission::Reparent);
        assert_eq!(
            result,
            PermissionCheckResult {
                granted: false,
                audit: true,
                permissive: false,
                todo_bug: None
            }
        );
        assert!(!result.permit());
    }
}