ksmbd: close durable scavenger races against m_fp_list lookups

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Summary

CVECVE-2026-64142
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 16:17:56 UTC
Updated2026-07-19 16:17:56 UTC
DescriptionIn 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---

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 7f0cb478703cbeaddfe5c9101c5c73cd975d1073 3a436932eb397e909d0607d76a8325abd9d85a35 git Not specified
CNA Linux Linux affected d484d621d40f4a8b8959008802d79bef3609641b 95f072ef934ca00711d510676b8792cbf59a5aae git Not specified
CNA Linux Linux affected d484d621d40f4a8b8959008802d79bef3609641b 5da69a65b282d2276de22e5194ba0f88c836170c git Not specified
CNA Linux Linux affected d484d621d40f4a8b8959008802d79bef3609641b 1f8f3246d55f89350a1a67bdf3744b7241048e4e git Not specified
CNA Linux Linux affected d484d621d40f4a8b8959008802d79bef3609641b bf736184d063da1a552ffeff0481813599a182cc git Not specified
CNA Linux Linux affected 6.11 Not specified
CNA Linux Linux unaffected 6.11 semver Not specified
CNA Linux Linux unaffected 6.12.92 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.34 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.11 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5da69a65b282d2276de22e5194ba0f88c836170c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bf736184d063da1a552ffeff0481813599a182cc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3a436932eb397e909d0607d76a8325abd9d85a35 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1f8f3246d55f89350a1a67bdf3744b7241048e4e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/95f072ef934ca00711d510676b8792cbf59a5aae 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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