CVE-2026-64437 — linux / linux_kernel
Use After FreeIn the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL
Commit f580d27e8928 ("ksmbd: fix use-after-free of a deferred file_lock on double SMB2_CANCEL") made smb2_cancel() skip a work whose state is KSMBD_WORK_CANCELLED, so its cancel_fn cannot be fired a second time. But KSMBD_WORK has three states (ACTIVE, CANCELLED, CLOSED), and the same freeing producer path is reached for CLOSED too:
SMB2_CLOSE on the locking handle -> set_close_state_blocked_works() sets the deferred work's state to KSMBD_WORK_CLOSED and wakes the smb2_lock() worker. The worker takes the non-ACTIVE early-exit, locks_free_lock()s the file_lock and, because the state is not KSMBD_WORK_CANCELLED, takes the STATUS_RANGE_NOT_LOCKED branch with "goto out2" -- which, like the cancelled branch, skips release_async_work(). The work stays on conn->async_requests with a live cancel_fn = smb2_remove_blocked_lock pointing at the freed file_lock.
A subsequent SMB2_CANCEL for the same AsyncId then passes the KSMBD_WORK_CANCELLED-only guard (its state is KSMBD_WORK_CLOSED), so smb2_cancel() fires cancel_fn again over the freed file_lock -- the same use-after-free fixed, via SMB2_CLOSE instead of a first SMB2_CANCEL:
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 (non-ACTIVE early-exit) ... cache file_lock_cache of size 192
Reproduced on mainline 7.1-rc7 (which already contains f580d27e8928) with KASAN by an authenticated SMB client; the double-SMB2_CANCEL control is silent on that kernel, so the splat is attributable to the CLOSE trigger.
Only an ACTIVE deferred work may have its cancel_fn fired: both terminal states (CANCELLED and CLOSED) reach the smb2_lock() early-exit that frees the file_lock and skips release_async_work(). Guard on KSMBD_WORK_ACTIVE so any non-active work is skipped.
| Software | Affected versions |
|---|---|
| linux / linux_kernel | >= 6.1.176, < 6.1.178 |
| linux / linux_kernel | >= 6.6.143, < 6.6.145 |
| linux / linux_kernel | >= 6.12.94, < 6.12.96 |
| linux / linux_kernel | >= 6.18.36, < 6.18.39 |
| linux / linux_kernel | >= 7.0.13, < 7.1 |
| linux / linux_kernel | >= 7.1.1, < 7.1.4 |
| linux / linux_kernel | = 7.1 |
| linux / linux_kernel | = 7.1-rc7 |
- https://git.kernel.org/stable/c/10f293a07f9e10e988b0ae44e2e99c631f5a68e0
- https://git.kernel.org/stable/c/12c36c99655f325befe50c26842f7deca414c381
- https://git.kernel.org/stable/c/94083db751930b1540ddff2b54d4677549c57f81
- https://git.kernel.org/stable/c/a796ba4e61d5e14e07b79a359faac69f8f9b22a3
- https://git.kernel.org/stable/c/b8e274e69ab09222c7a552c7c0c1eef9ce627fc1
- https://git.kernel.org/stable/c/ddb9239828336b36d8a3ef5943fdffb2f55b6508
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