The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x 3cad1bc010416c6dd780643476bc59ed742436b9 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024070802-nebula-stir-11eb@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

3cad1bc01041 ("filelock: Remove locks reliably when fcntl/close race is detected") 4ca52f539865 ("filelock: have fs/locks.c deal with file_lock_core directly") a69ce85ec9af ("filelock: split common fields into struct file_lock_core") 3d40f78169a0 ("filelock: drop the IS_* macros") 75cabec0111b ("filelock: add some new helper functions") 587a67b6830b ("filelock: rename some fields in tracepoints") 0e9876d8e88d ("filelock: fl_pid field should be signed int") 6c9007f65d14 ("fs/locks: F_UNLCK extension for F_OFD_GETLK") dc592190a554 ("fs/locks: Remove redundant assignment to cmd") 3822a7c40997 ("Merge tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3cad1bc010416c6dd780643476bc59ed742436b9 Mon Sep 17 00:00:00 2001 From: Jann Horn jannh@google.com Date: Tue, 2 Jul 2024 18:26:52 +0200 Subject: [PATCH] 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@googl... Reviewed-by: Jeff Layton jlayton@kernel.org Signed-off-by: Christian Brauner brauner@kernel.org

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; } }