feat(jailer): add Landlock LSM sandbox with composable Sandbox API#416
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Redesign the Sandbox trait from `wrap() -> Command` to `apply(&mut Command)` enabling natural composition of multiple isolation layers. New architecture: - BwrapSandbox: namespace isolation + cgroup join (replaces cmd + adds pre_exec) - LandlockSandbox: filesystem/network ACL (adds Landlock pre_exec) - CompositeSandbox: chains N sandboxes via Vec<Box<dyn Sandbox>> - Linux PlatformSandbox = CompositeSandbox([BwrapSandbox, LandlockSandbox]) Landlock (kernel 5.13+) adds inode-based filesystem restrictions as defense-in-depth, complementing bwrap namespaces and seccomp syscall filtering. Degrades gracefully on older kernels (BestEffort mode logs warning and continues). Key design: split parent/child pattern for zero-gap enforcement. Parent builds the Landlock ruleset (full crate API, allocates freely), child applies via single landlock_restrict_self() syscall in pre_exec (async-signal-safe).
Replace the trivial restrict_self_in_thread test with a real e2e test that: 1. Creates a temp directory with a test file 2. Builds a Landlock ruleset allowing only that directory 3. Applies the restriction via restrict_self_raw 4. Verifies: allowed file is readable, allowed dir is writable 5. Verifies: home directory access is DENIED (EACCES)
- test_landlock_readonly_denies_write: verifies writable:false allows read but denies write (EACCES) - test_landlock_multiple_paths_enforcement: 3 dirs with different access levels, verifies each - test_landlock_network_deny: verifies network_enabled=false blocks TCP (graceful on < 6.7)
Landlock rules are hierarchical — /tmp has system write access, so subdirs inherit that regardless of per-path restrictions. Use dirs under $HOME instead, which are outside the system path ruleset.
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Summary
Sandboxtrait fromwrap() -> Commandtoapply(&mut Command), enabling natural composition of multiple isolation layersLandlockSandbox— Linux Landlock LSM for inode-based filesystem/network access control (kernel 5.13+)CompositeSandbox— chains N sandboxes viaVec<Box<dyn Sandbox>>, each modifying the sameCommandin orderPlatformSandboxis nowCompositeSandbox([BwrapSandbox, LandlockSandbox])— bwrap handles namespaces, Landlock handles filesystem ACLlandlock_restrict_self()syscall inpre_exec(async-signal-safe, zero-gap enforcement)Test plan
#[cfg(target_os = "linux")])cargo clippy -- -D warningsclean on both platforms