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| author | Jann Horn <jannh@google.com> | 2024-07-02 18:26:52 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-07-02 20:48:14 +0200 |
| commit | 3cad1bc010416c6dd780643476bc59ed742436b9 (patch) | |
| tree | dbf3cf60020c62045370a96a0ec4450cbe8265e2 /fs | |
| parent | 22a40d14b572deb80c0648557f4bd502d7e83826 (diff) | |
| download | linux-stable-3cad1bc010416c6dd780643476bc59ed742436b9.tar.gz linux-stable-3cad1bc010416c6dd780643476bc59ed742436b9.tar.bz2 linux-stable-3cad1bc010416c6dd780643476bc59ed742436b9.zip | |
filelock: Remove locks reliably when fcntl/close race is detected
When fcntl_setlk() races with close(), it removes the created lock with
do_lock_file_wait().
However, LSMs can allow the first do_lock_file_wait() that created the lock
while denying the second do_lock_file_wait() that tries to remove the lock.
In theory (but AFAIK not in practice), posix_lock_file() could also fail to
remove a lock due to GFP_KERNEL allocation failure (when splitting a range
in the middle).
After the bug has been triggered, use-after-free reads will occur in
lock_get_status() when userspace reads /proc/locks. This can likely be used
to read arbitrary kernel memory, but can't corrupt kernel memory.
This only affects systems with SELinux / Smack / AppArmor / BPF-LSM in
enforcing mode and only works from some security contexts.
Fix it by calling locks_remove_posix() instead, which is designed to
reliably get rid of POSIX locks associated with the given file and
files_struct and is also used by filp_flush().
Fixes: c293621bbf67 ("[PATCH] stale POSIX lock handling")
Cc: stable@kernel.org
Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=2563
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20240702-fs-lock-recover-2-v1-1-edd456f63789@google.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/locks.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/fs/locks.c b/fs/locks.c index 90c8746874de..c360d1992d21 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -2448,8 +2448,9 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, error = do_lock_file_wait(filp, cmd, file_lock); /* - * Attempt to detect a close/fcntl race and recover by releasing the - * lock that was just acquired. There is no need to do that when we're + * Detect close/fcntl races and recover by zapping all POSIX locks + * associated with this file and our files_struct, just like on + * filp_flush(). There is no need to do that when we're * unlocking though, or for OFD locks. */ if (!error && file_lock->c.flc_type != F_UNLCK && @@ -2464,9 +2465,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, f = files_lookup_fd_locked(files, fd); spin_unlock(&files->file_lock); if (f != filp) { - file_lock->c.flc_type = F_UNLCK; - error = do_lock_file_wait(filp, cmd, file_lock); - WARN_ON_ONCE(error); + locks_remove_posix(filp, files); error = -EBADF; } } |