The mkdir->rename->remove->rename directory fallback had a TOCTOU window
between the second remove and the second rename: a concurrent writer
creating an entry at the destination was silently clobbered. The fallback
now claims the destination once with mkdir and never unlinks it: the
fast-path rename publishes over the claim (Linux), and platforms that
refuse directory renames (macOS, Windows) move the staged children into
the claim through atomic no-clobber primitives (mkdir/os.Link/os.Symlink),
consuming the emptied source shell on success.
renameSkillPathNoReplace now returns the mkdir-claim identity captured by
the child-move path. PublishSkillPathNoReplace uses it as a three-state
ownership witness: the atomic/fast paths keep the staged-inode proof, the
child-move path proves dest is still the mkdir claim, and a mismatch
reports the new ErrSkillPathPublicationUncertain sentinel with the
destination retained. The witness is real on POSIX now: darwin and linux
report the dev:ino file identity instead of the empty no-op.
Upstream consumers honor the sentinel: the mono/multi upgrade copy
fallbacks no longer retry over an uncertain destination (the retry would
displace the concurrent writer's object), and skill setup reports the
retained destination instead of claiming a rollback.
Rewrites the fallback tests that pinned the removed remove-and-retry flow
and adds regression coverage: concurrent claim entries abort with the
destination retained, wholesale replacement after child-move reports the
uncertain sentinel, staged-set transactions pass the sentinel through,
and both copy fallbacks short-circuit (ablation-verified).
Add FILE_FLAG_OPEN_REPARSE_POINT to the Windows CreateFile call in
skillPathFileIdentityImpl so symlinks are opened as reparse points
rather than followed to their target. Staged symlinks carry relative
targets computed for the final destination, which may not resolve from
the staging directory; following them caused CreateFile to fail,
yielding an empty file ID that rejected publication and broke canonical
skill layout migration on Windows.
Make skillPathSameFileIdentity a seam variable so the tunneled
replacement test can deterministically simulate the identity change on
Unix. On tmpfs (used by Linux CI runners), os.SameFile can return true
for a recreated file due to inode reuse, making the test flaky. On
Windows the swap is a no-op because skillPathIdentityProven compares
file IDs from GetFileInformationByHandle and ignores
skillPathSameFileIdentity.
NTFS file tunneling can restore the original creation time for a
recreated same-named object, which defeated the creation-time
incarnation check and allowed rollback to delete a concurrent
replacement. Replace the platform-specific identity pair with a single
skillPathIdentityProven function:
- Unix: delegates to os.SameFile (inode/dev), ignoring file ID strings
- Windows: compares VolumeSerialNumber:FileIndexHigh:FileIndexLow from
GetFileInformationByHandle, which uniquely identifies the file on the
volume for its lifetime and is unaffected by tunneling
When the file ID cannot be obtained at publish time, identity is not
proven and the auto-delete is refused. Add a regression test that
simulates tunneled creation time and verifies rollback still refuses
the concurrent replacement.
The fallback path for filesystems without RENAME_NOREPLACE/EXCL (NFS,
FUSE, overlayfs) used Lstat-then-Rename, which could overwrite a
concurrently created destination between the check and the rename.
Replace the TOCTOU-prone check with truly atomic no-clobber primitives:
- Directories: os.Mkdir atomically claims the destination (fails with
EEXIST if occupied). On Linux rename(2) replaces the empty dir
directly; on Darwin/Windows rename refuses existing dirs so the empty
dir is removed and the rename retried — any concurrent creation
between remove and rename is detected by the second rename failing.
- Files: os.Link atomically fails if the destination exists, then
os.Remove completes the move.
Add concurrent-creation test covering the mkdir→rename race window.
玉澜