secure_walk_at() has two fast paths for the final component that call
openat(ds_cur(&ds), part, ...) directly instead of going through
ds_descend(). A final component of ".." therefore never met the anchor
floor, and what happened depended entirely on the caller's flags:
".." with O_DIRECTORY -> ELOOP (refused)
".." with O_DIRECTORY|O_NOFOLLOW -> fd for the directory ABOVE
the anchor
".." without O_DIRECTORY -> parent opened, then closed,
EISDIR returned
That was harmless while every literal ".." was rejected at the front
door, but secure_relative_open_at_beneath() now admits them and
documents the held-fd stack as refusing every climb above the anchor.
The sender's own call passes O_RDONLY|O_DIRECTORY and so was never
affected -- but the guarantee the new API advertises has to hold for
whatever flags the next caller picks.
Route a literal "." or ".." through ds_descend() before the leaf fast
paths. All three flag combinations now refuse a bare ".." with ELOOP,
and t_secure_relpath covers the matrix.
Add the rest of the path-based syscall wrappers and migrate every
receiver-side caller:
- do_lchown_at, do_rename_at, do_mkdir_at, do_symlink_at,
do_mknod_at, do_link_at, do_unlink_at, do_rmdir_at,
do_utimensat_at, do_stat_at, do_lstat_at
Same shape as do_chmod_at: open each parent under
secure_relative_open(), call the *at() variant against the dirfd,
fall through to the bare path-based syscall in non-daemon /
chrooted / absolute-path / no-parent cases. macOS's
setattrlist-based set_times tier is also routed through the
utimensat_at path on daemon-no-chroot.
Hardenings to secure_relative_open() itself:
- confine basedir resolution under the same kernel mechanism
used for relpath (basedirs from --copy-dest / --link-dest are
sender-controllable in daemon mode)
- reject any '..' component (bare '..', 'foo/..', 'subdir/..')
so the per-component O_NOFOLLOW fallback can't escape
- return the dirfd we built up from the per-component fallback
when the caller passed O_DIRECTORY (otherwise every do_*_at
failed with EINVAL on platforms without RESOLVE_BENEATH)
Adds testsuite/alt-dest-symlink-race.test and
testsuite/secure-relpath-validation.test (with t_secure_relpath
helper) as regression coverage for the new hardenings.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Zen Dodd