CVE-2026-64142In the Linux kernel, the following vulnerability has been resolved: ksmbd: close durable scavenger races against m_fp_list lookups ksmbd_durable_scavenger() has two related races against any walker t…

In the Linux kernel, the following vulnerability has been resolved: ksmbd: close durable scavenger races against m_fp_list lookups ksmbd_durable_scavenger() has two related races against any walker that iterates f_ci->m_fp_list, including ksmbd_lookup_fd_inode() (used by ksmbd_vfs_rename) and the share-mode checks in fs/smb/server/smb_common.c. (1) fp->node list-head reuse. Durable-preserved handles can remain linked on f_ci->m_fp_list after session teardown so share-mode checks still see them while the handle is reconnectable. The scavenger collected expired handles by adding fp->node to a local scavenger_list after removing them from the global durable idr. Because fp->node is the same list_head used by m_fp_list, list_add(&fp->node, &scavenger_list) overwrites the m_fp_list links and corrupts both lists. CONFIG_DEBUG_LIST can report this on the share-mode walk path. (2) Refcount race against m_fp_list walkers. The scavenger qualifies an expired durable handle with atomic_read(&fp->refcount) > 1 and fp->conn under global_ft.lock, removes fp from global_ft, then drops global_ft.lock before unlinking fp from m_fp_list and freeing it. During that gap fp is still linked on m_fp_list with f_state == FP_INITED. ksmbd_lookup_fd_inode() under m_lock read calls ksmbd_fp_get() (atomic_inc_not_zero on refcount that is still 1) and takes a live reference; the scavenger then unlinks and frees fp while the holder owns a reference, leading to UAF on the holder's subsequent ksmbd_fd_put() and on any field reads performed by a concurrent share-mode walker that iterates m_fp_list without taking ksmbd_fp_get() (smb_check_perm_dleases-like paths). Fix both: * Stop reusing fp->node as a scavenger-private list node. Remove one expired handle from global_ft under global_ft.lock, take an explicit transient reference, drop the lock, unlink fp->node from m_fp_list under f_ci->m_lock, then drop both the durable lifetime and transient references with atomic_sub_and_test(2, &fp->refcount). If the scavenger is the last putter the close runs there; otherwise an in-flight holder that already raced through the m_fp_list lookup owns the final close via its ksmbd_fd_put() path. The one-at-a-time disposal can rescan the durable idr when multiple handles expire in the same pass, but durable scavenging is a background expiration path and the final full scan recomputes min_timeout before the next wait. * Clear fp->persistent_id inside __ksmbd_remove_durable_fd() right after idr_remove(), so a delayed final close from a holder that snatched fp does not re-issue idr_remove() on a persistent id that idr_alloc_cyclic() in ksmbd_open_durable_fd() may have already handed out to a brand-new durable handle. * Bypass the per-conn open_files_count decrement in __put_fd_final() when fp is detached from any session table (fp->conn cleared by session_fd_check() at durable preserve -- paired with the volatile_id clear at unpublish, so checking fp->conn alone is sufficient). The walker that owns the final close runs from an unrelated work->conn whose stats.open_files_count never tracked this durable fp; without this guard the holder would underflow that unrelated counter. The two races are folded into one patch because patch (1) alone cleans up the corrupted list but leaves a deterministic UAF window for m_fp_list walkers that the transient-reference and persistent_id discipline in (2) close; bisecting onto an intermediate state would land on a UAF that pre-patch chaos merely made less reproducible. Validation: * CONFIG_DEBUG_LIST coverage for the list_head reuse path. * KASAN-enabled direct SMB2 durable-handle coverage that exercised ksmbd_durable_scavenger() and non-NULL ksmbd_lookup_fd_inode() returns while durable handles expired under concurrent rename lookups, with no KASAN, UAF, list-corruption, ODEBUG, or WARNING reports. ---truncated---

CVSS

9.8 CRITICAL (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness (CWE)

CWE-416

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

Not given

NVD analysis

Analyzed

Record last updated

Aug 17, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

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