CVE-2026-64378writeback: fix race between cgroup_writeback_umount() and inode_switch_wbs()
- 7.8HighCVSS base score
- 0.10%Exploitation in 30 daysEPSS · top 99% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
In the Linux kernel, the following vulnerability has been resolved: writeback: fix race between cgroup_writeback_umount() and inode_switch_wbs() When a container exits, the following BUG_ON() is occasionally triggered: ================================================================== VFS: Busy inodes after unmount of sdb (ext4) ------------[ cut here ]------------ kernel BUG at fs/super.c:695! CPU: 3 PID: 6 Comm: containerd-shim Tainted: G OE K 6.6 #1 pstate: 63400009 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--) pc : generic_shutdown_super+0xf0/0x100 lr : generic_shutdown_super+0xf0/0x100 Call trace: generic_shutdown_super+0xf0/0x100 kill_block_super+0x20/0x48 ext4_kill_sb+0x28/0x60 deactivate_locked_super+0x54/0x130 deactivate_super+0x84/0xa0 cleanup_mnt+0xa4/0x140 __cleanup_mnt+0x18/0x28 task_work_run+0x78/0xe0 do_notify_resume+0x204/0x240 ================================================================== The root cause is a race between cgroup_writeback_umount() and inode_switch_wbs()/cleanup_offline_cgwb(). There is a window between inode_prepare_wbs_switch() returning true and the subsequent wb_queue_isw() call. Following is the process that triggers the issue: CPU A (umount) | CPU B (writeback) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ inode_switch_wbs/cleanup_offline_cgwb atomic_inc(&isw_nr_in_flight) inode_prepare_wbs_switch -> passes SB_ACTIVE check __iget(inode) generic_shutdown_super sb->s_flags &= ~SB_ACTIVE cgroup_writeback_umount(sb) smp_mb() atomic_read(&isw_nr_in_flight) rcu_barrier() -> no pending RCU callbacks flush_workqueue(isw_wq) -> nothing queued, returns evict_inodes(sb) -> Inode skipped as isw still holds a ref. sop->put_super(sb) /* destroys percpu counters */ -> VFS: Busy inodes after unmount! wb_queue_isw() queue_work(isw_wq, ...) /* later in work function */ inode_switch_wbs_work_fn process_inode_switch_wbs iput() -> evict percpu_counter_dec() // UAF! Fix this by extending the RCU read-side critical section in inode_switch_wbs() and cleanup_offline_cgwb() to cover from inode_prepare_wbs_switch() through wb_queue_isw(). Since there is no sleep in this window, rcu_read_lock() can be used. Then add a synchronize_rcu() in cgroup_writeback_umount() before the existing rcu_barrier(), so that all in-flight switchers that have passed the SB_ACTIVE check have completed queue_work() before flush_workqueue() is called. The existing rcu_barrier() is intentionally retained so this fix can be backported unchanged to stable kernels (5.10.y, 6.6.y, ...) that still queue switches via queue_rcu_work(). It is a no-op on current mainline (since commit e1b849cfa6b6 ("writeback: Avoid contention on wb->list_lock when switching inodes")) and is removed in a follow-up patch.
Timeline
ID reserved
By Linux
- 6 days later
· 6 days later
Published
- 3 months later
· 3 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Modified | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.10% · top 99% of all CVEs (15 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.
Affected products
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < 087d5b8b501c570f84bf655164e6698c3ce146e0
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < 3c9c9648f77e4d14e50676bc51c2174ba9c8d361
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < 5c3265f3252b2ee50707adaaa3f9bd0df3df72de
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < c923cc3cb5cd8945ceaf08252754110643446593
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < 685fc15a410885b6d4dee64de0dce721b9428b12
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < 53eeaf4d63068dbc7708b0c7adb20151c812feca
- affected a1a0e23e49037c23ea84bc8cc146a03584d13577 – < cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d
- affected c5cbbec54fe71c4de2d34f8c0ec8fbfdd7f17339
- affected 4.4.5 – < 4.5
- affected 4.5
- unaffected < 4.5
- unaffected 5.10.261 – ≤ 5.10.*
- unaffected 6.1.178 – ≤ 6.1.*
- unaffected 6.6.145 – ≤ 6.6.*
- unaffected 6.12.96 – ≤ 6.12.*
- unaffected 6.18.39 – ≤ 6.18.*
- unaffected 7.1.4 – ≤ 7.1.*
- unaffected 7.2 – ≤ *
References
References7
- https://git.kernel.org/stable/c/087d5b8b501c570f84bf655164e6698c3ce146e0 (opens in a new tab)
- https://git.kernel.org/stable/c/3c9c9648f77e4d14e50676bc51c2174ba9c8d361 (opens in a new tab)
- https://git.kernel.org/stable/c/5c3265f3252b2ee50707adaaa3f9bd0df3df72de (opens in a new tab)
- https://git.kernel.org/stable/c/c923cc3cb5cd8945ceaf08252754110643446593 (opens in a new tab)
- https://git.kernel.org/stable/c/685fc15a410885b6d4dee64de0dce721b9428b12 (opens in a new tab)
- https://git.kernel.org/stable/c/53eeaf4d63068dbc7708b0c7adb20151c812feca (opens in a new tab)
- https://git.kernel.org/stable/c/cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-48922 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
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[](https://cveledger.app/cve/CVE-2026-64378)Record last updated .