fix(mount): copy xattr value bytes to avoid FUSE buffer aliasing (#9275)
SetXAttr stored the caller-supplied `data` slice directly into
entry.Extended. That slice aliases go-fuse's per-request input buffer,
which is returned to a pool the moment the handler returns. When a file
is open during setxattr (the open-fh path defers persistence to flush),
the next FUSE request recycles the buffer and silently overwrites the
stored xattr bytes; flushMetadataToFiler then ships the corrupted bytes
to the filer. `cp -a` reproduces this because it issues a setxattr while
holding an open fh, then continues to issue follow-up FUSE ops that
reuse the same buffer.
The path-based setxattr (e.g. setfattr without an open fh) saves
synchronously inside the same handler, so the bytes were marshalled
before the buffer could be reused — that is why the source file in the
report looked fine and only the cp -a destination was garbage.
Defensively copy the bytes when storing them, and add a unit test that
mutates the caller buffer after SetXAttr returns to lock in the
invariant.
7a461ffc2f