filelock: Remove locks reliably when fcntl/close race is detected

stable inclusion
from stable-v4.19.316
commit d30ff33040834c3b9eee29740acd92f9c7ba2250
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAF3IR
CVE: CVE-2024-41012

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.19.y&id=d30ff33040834c3b9eee29740acd92f9c7ba2250

--------------------------------

commit 3cad1bc010416c6dd780643476bc59ed742436b9 upstream.

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: c293621b ("[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>
[stable fixup: ->c.flc_type was ->fl_type in older kernels]
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Long Li <leo.lilong@huawei.com>