CVE-2026-53198

Summary

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 out"s 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.

Affected Software

Weaknesses

References

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

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