GHSA-X5P7-HG5V-9P54
Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-27 06:30In 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.
{
"affected": [],
"aliases": [
"CVE-2026-64437"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-25T10:17:28Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL\n\nCommit f580d27e8928 (\"ksmbd: fix use-after-free of a deferred file_lock on\ndouble SMB2_CANCEL\") made smb2_cancel() skip a work whose state is\nKSMBD_WORK_CANCELLED, so its cancel_fn cannot be fired a second time. But\nKSMBD_WORK has three states (ACTIVE, CANCELLED, CLOSED), and the same\nfreeing producer path is reached for CLOSED too:\n\n SMB2_CLOSE on the locking handle -\u003e set_close_state_blocked_works() sets\n the deferred work\u0027s state to KSMBD_WORK_CLOSED and wakes the smb2_lock()\n worker. The worker takes the non-ACTIVE early-exit, locks_free_lock()s\n the file_lock and, because the state is not KSMBD_WORK_CANCELLED, takes\n the STATUS_RANGE_NOT_LOCKED branch with \"goto out2\" -- which, like the\n cancelled branch, skips release_async_work(). The work stays on\n conn-\u003easync_requests with a live cancel_fn = smb2_remove_blocked_lock\n pointing at the freed file_lock.\n\nA subsequent SMB2_CANCEL for the same AsyncId then passes the\nKSMBD_WORK_CANCELLED-only guard (its state is KSMBD_WORK_CLOSED), so\nsmb2_cancel() fires cancel_fn again over the freed file_lock -- the same\nuse-after-free fixed, via SMB2_CLOSE instead of a first SMB2_CANCEL:\n\n BUG: KASAN: slab-use-after-free in __locks_delete_block\n __locks_delete_block\n locks_delete_block\n ksmbd_vfs_posix_lock_unblock\n smb2_remove_blocked_lock\n smb2_cancel \u003c- 2nd SMB2_CANCEL fires cancel_fn\n handle_ksmbd_work\n Allocated by ...: locks_alloc_lock \u003c- smb2_lock\n Freed by ...: locks_free_lock \u003c- smb2_lock (non-ACTIVE early-exit)\n ... cache file_lock_cache of size 192\n\nReproduced on mainline 7.1-rc7 (which already contains f580d27e8928) with\nKASAN by an authenticated SMB client; the double-SMB2_CANCEL control is\nsilent on that kernel, so the splat is attributable to the CLOSE trigger.\n\nOnly an ACTIVE deferred work may have its cancel_fn fired: both terminal\nstates (CANCELLED and CLOSED) reach the smb2_lock() early-exit that frees\nthe file_lock and skips release_async_work(). Guard on KSMBD_WORK_ACTIVE\nso any non-active work is skipped.",
"id": "GHSA-x5p7-hg5v-9p54",
"modified": "2026-07-27T06:30:37Z",
"published": "2026-07-25T12:31:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64437"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/10f293a07f9e10e988b0ae44e2e99c631f5a68e0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/12c36c99655f325befe50c26842f7deca414c381"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/94083db751930b1540ddff2b54d4677549c57f81"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a796ba4e61d5e14e07b79a359faac69f8f9b22a3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b8e274e69ab09222c7a552c7c0c1eef9ce627fc1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ddb9239828336b36d8a3ef5943fdffb2f55b6508"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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