The SDK's built-in Bash tool ran commands as a bare subprocess with only
current_dir set — no OS boundary. On a server that let an agent shell read
/etc/shadow, cd /, write anywhere the process uid could, and reach the
network; the phase-1 path validation only guards the file tools, not bash.
(The SDK's SandboxSettings is dead config: Agent::new never reads it.)
Replace it with SandboxedBashTool — same name and input schema, registered
via custom_tools so it overrides the built-in by name — that confines the
command with bubblewrap, gated by permission mode:
- Default / AcceptEdits (review modes): run inside a bwrap namespace with the
system mounted read-only, the session sandbox dir bind-mounted rw at its
real path and made the cwd, /etc //root //home and all other host paths
absent, and --unshare-all (network included). Filesystem escape and network
egress are blocked by the kernel, not by convention.
- FullAccess (explicitly dangerous): unconfined, same as before, but every
command is audit-logged with a warning.
Fail-closed: in a review mode, if bwrap is unavailable the command is refused
rather than silently run unconfined — no fabricated boundary.
Verified end-to-end in tests/agent_bash_sandbox.rs by invoking the tool:
under Default mode `cat /etc/passwd` sees no host passwd, `ls /` exposes no
etc//root//home, a write to /etc/cron.d/x fails (and the host file is never
created), and the network is unreachable; in-sandbox work succeeds and lands
in the real session dir; FullAccess can see the host. bwrap 0.11.2 confirmed
functional on this host (root, CAP_SYS_ADMIN, user namespaces enabled).
Phase-1 suites stay green.
boos
b0ce83a937