The chmod-symlink-race test was previously a no-op on Solaris,
OpenBSD, NetBSD, and Cygwin via a case 'uname -s' skip. The skip
was too broad: of the four scenarios the helper exercises, only
the 'legitimate within-tree dir-symlink' one actually needs
RESOLVE_BENEATH-equivalent kernel support. The other three
(attack rejection, plain relative path, top-level file) behave
identically on the per-component O_NOFOLLOW fallback and would
have caught the t_stub.c max_alloc=0 bug fixed in the previous
commit if the test had been allowed to run.
Make the helper probe the running kernel for either
openat2(RESOLVE_BENEATH) on Linux 5.6+ or openat(O_RESOLVE_BENEATH)
on FreeBSD 13+ / macOS 15+ by opening '.' under the requested
confinement. Honour the result:
- If RESOLVE_BENEATH-equivalent confinement is available, the
within-tree symlink scenario must succeed (status quo).
- If not, the per-component O_NOFOLLOW fallback rejects every
symlink including legitimate ones; expect the within-tree
symlink scenario to be rejected (rc != 0) and the file mode
to remain unchanged.
The attack-rejection, plain-path and top-level scenarios are
unchanged: they expect the same outcome on both code paths.
Drop the case-based skip from chmod-symlink-race.test so the test
runs everywhere and the per-component fallback gets the CI
coverage that the SunOS/OpenBSD/NetBSD/Cygwin runners can
provide. HPE NonStop -- which lacks RESOLVE_BENEATH but isn't in
the existing skip list -- is also covered by this change.
CVE-2026-29518's fix routed the receiver's open() through
secure_relative_open(), but every other path-based syscall the
receiver runs on sender-controllable paths is vulnerable to the
same TOCTOU primitive. This commit closes the chmod variant.
Add do_chmod_at() that opens the parent of fname under
secure_relative_open() and uses fchmodat() against the resulting
dirfd. Gate the secure path on am_daemon && !am_chrooted (the same
gate use_secure_symlinks already uses for the receiver basis-file
open), so non-daemon callers and chrooted daemons keep the original
do_chmod() fast path.
Migrate the receiver-side do_chmod() call sites in delete.c,
generator.c, rsync.c, and xattrs.c.
Adds testsuite/chmod-symlink-race.test (with t_chmod_secure helper)
as regression coverage.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
