Bug 2414745 (CVE-2025-40196)

Summary: CVE-2025-40196 kernel: fs: quota: create dedicated workqueue for quota_release_work
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A workqueue configuration mismatch was found in the Linux kernel's filesystem quota subsystem during writeback operations. A local user can trigger this issue when f2fs filesystem balancing initiates quota writeback during sync operations, causing the writeback workqueue to flush quota_release_work from the events_unbound queue. Since events_unbound lacks the WQ_MEM_RECLAIM flag while the writeback queue has it, this flag mismatch triggers workqueue dependency warnings and causes kernel panic when panic_on_warn is enabled, resulting in denial of service.
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Description OSIDB Bzimport 2025-11-12 23:04:03 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fs: quota: create dedicated workqueue for quota_release_work

There is a kernel panic due to WARN_ONCE when panic_on_warn is set.

This issue occurs when writeback is triggered due to sync call for an
opened file(ie, writeback reason is WB_REASON_SYNC). When f2fs balance
is needed at sync path, flush for quota_release_work is triggered.
By default quota_release_work is queued to "events_unbound" queue which
does not have WQ_MEM_RECLAIM flag. During f2fs balance "writeback"
workqueue tries to flush quota_release_work causing kernel panic due to
MEM_RECLAIM flag mismatch errors.

This patch creates dedicated workqueue with WQ_MEM_RECLAIM flag
for work quota_release_work.

------------[ cut here ]------------
WARNING: CPU: 4 PID: 14867 at kernel/workqueue.c:3721 check_flush_dependency+0x13c/0x148
Call trace:
 check_flush_dependency+0x13c/0x148
 __flush_work+0xd0/0x398
 flush_delayed_work+0x44/0x5c
 dquot_writeback_dquots+0x54/0x318
 f2fs_do_quota_sync+0xb8/0x1a8
 f2fs_write_checkpoint+0x3cc/0x99c
 f2fs_gc+0x190/0x750
 f2fs_balance_fs+0x110/0x168
 f2fs_write_single_data_page+0x474/0x7dc
 f2fs_write_data_pages+0x7d0/0xd0c
 do_writepages+0xe0/0x2f4
 __writeback_single_inode+0x44/0x4ac
 writeback_sb_inodes+0x30c/0x538
 wb_writeback+0xf4/0x440
 wb_workfn+0x128/0x5d4
 process_scheduled_works+0x1c4/0x45c
 worker_thread+0x32c/0x3e8
 kthread+0x11c/0x1b0
 ret_from_fork+0x10/0x20
Kernel panic - not syncing: kernel: panic_on_warn set ...
Comment 1 Alexander B 2025-11-13 10:16:25 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025111245-CVE-2025-40196-f1fa@gregkh/T