CVE-2026-53198

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free of a deferred file_lock on double SMB2_CANCEL

A deferred byte-range lock (an SMB2_LOCK that blocks) registers an async work on conn->async_requests via setup_async_work(), with cancel_fn = smb2_remove_blocked_lock and cancel_argv[0] pointing at the struct file_lock.

When the request is cancelled, the worker frees the file_lock with locks_free_lock() and takes the cancelled early-exit, which goto outs and never reaches release_async_work() – the only site that unlinks the work from conn->async_requests and clears cancel_fn/cancel_argv. The work therefore stays matchable on async_requests with a live cancel_fn pointing at the freed file_lock, until connection teardown finally runs release_async_work().

smb2_cancel() fires cancel_fn unconditionally with no state guard, so a second SMB2_CANCEL for the same AsyncId, arriving in that window, re-runs smb2_remove_blocked_lock() on the freed file_lock – a slab use-after-free:

BUG: KASAN: slab-use-after-free in __locks_delete_block __locks_delete_block locks_delete_block ksmbd_vfs_posix_lock_unblock smb2_remove_blocked_lock smb2_cancel <- 2nd SMB2_CANCEL fires cancel_fn handle_ksmbd_work Allocated by …: locks_alloc_lock <- smb2_lock Freed by …: locks_free_lock <- smb2_lock (cancelled branch) … cache file_lock_cache of size 192

Reproduced on mainline with KASAN by an authenticated SMB client.

Skip a work whose state is already KSMBD_WORK_CANCELLED so its cancel callback cannot be fired a second time.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0da2e073f9cbf4985a0fd9acb71bc5ff599f8afd
• https://git.kernel.org/stable/c/14d2eee0193ac3cd1bf3d014373449f0b8d35d6d
• https://git.kernel.org/stable/c/2b2eda2821cff1d1b5a423b6ee7d8fc6fbc8e694
• https://git.kernel.org/stable/c/89ae9df09d2c1fb4a4eb495c113a7ce1dca34147
• https://git.kernel.org/stable/c/b7063c7426ea5a4d15e01b60538718765392f49d
• https://git.kernel.org/stable/c/f580d27e8928828693df44ba2db0fffdbe11dfea