CVE-2026-64142
Analyzed
Analyzed - Analysis Complete
Race Condition in ksmbd Leading to Use-After-Free in Linux Kernel
Vulnerability report for CVE-2026-64142, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-07-19
Last updated on: 2026-08-17
Assigner: kernel.org
Description
Description
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 Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| linux | linux_kernel | 7.1 |
| linux | linux_kernel | 7.1 |
| linux | linux_kernel | From 6.13 (inc) to 6.18.34 (exc) |
| linux | linux_kernel | From 6.19 (inc) to 7.0.11 (exc) |
| linux | linux_kernel | From 6.11 (inc) to 6.12.92 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-416 | The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. |
