sandbox: fail loudly when seccomp_unotify is requested but unusable - #285
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applyPolicy() installed the seccomp-unotify listener only when pipefd != -1. In modes that pass pipefd == -1 (e.g. MODE_STANDALONE_EXECVE) the install was silently skipped, and prepareAndCommit() then returned early because the classic seccomp filter is empty -- so a sandboxee for which seccomp_unotify was explicitly requested ran with NO seccomp policy at all, with no error emitted. Refuse to continue instead of silently dropping the requested policy: if seccomp_unotify is set but there is no supervisor to receive the notification fd (pipefd == -1), log an error and fail. Verified: `nsjail -Me --seccomp_unotify --seccomp_string 'DEFAULT ALLOW' -- ...` now aborts with a clear error instead of launching the process unfiltered.
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applyPolicy() installed the seccomp-unotify listener only when pipefd != -1. In modes that pass pipefd == -1 (e.g. MODE_STANDALONE_EXECVE) the install was silently skipped, and prepareAndCommit() then returned early because the classic seccomp filter is empty -- so a sandboxee for which seccomp_unotify was explicitly requested ran with NO seccomp policy at all, with no error emitted.
Refuse to continue instead of silently dropping the requested policy: if seccomp_unotify is set but there is no supervisor to receive the notification fd (pipefd == -1), log an error and fail.
Verified:
nsjail -Me --seccomp_unotify --seccomp_string 'DEFAULT ALLOW' -- ...now aborts with a clear error instead of launching the process unfiltered.