DAEMON's safepath-adversarial.md accepts a TOCTOU residual between its
canonicalise-and-check and the download starting, on the stated grounds
that CORE's O_NOFOLLOW open of the final file closes it. That flag was
never actually set: SparseFile::open used O_WRONLY|O_CREAT|O_CLOEXEC, so
a symlink swapped in as the final path component after DAEMON's check
would be followed and redirect our pwrites outside the allowed roots.
Add O_NOFOLLOW. A symlinked leaf now fails the open with ELOOP, which
errno_to_error already maps to Error::path_rejected. Regular files and
the O_CREAT of a fresh part file are unaffected; resume (existing regular
part file) is unaffected. Test that a symlinked destination is rejected
rather than silently followed, and that the link target is never touched.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HPPSGhiArbvQgwC2DNiURS
samiandClaude Sonnet 5
479f882324