Linux Kernel ksmbd SMB server Use-After-Free Rated 8.8 CVSS

Status: UPDATED  |  Advisory ID: CVE-2026-53198

Key Details

Affected Products, Subsystems & Sectors

What to Know

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. (NVD)

What to Do

Monitor Linux's and Siemens's web pages for any future patch releases.

References