CVE-2026-31586 (GCVE-0-2026-31586)
Vulnerability from cvelistv5 – Published: 2026-04-24 14:42 – Updated: 2026-04-27 14:04
VLAI?
Title
mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
Summary
In the Linux kernel, the following vulnerability has been resolved:
mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses
wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last
reference, the blkcg can be freed asynchronously (css_free_rwork_fn ->
blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the
pointer to access blkcg->online_pin, resulting in a use-after-free:
BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)
Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531
Workqueue: cgwb_release cgwb_release_workfn
Call Trace:
<TASK>
blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)
cgwb_release_workfn (mm/backing-dev.c:629)
process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)
Freed by task 1016:
kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)
css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)
process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)
** Stack based on commit 66672af7a095 ("Add linux-next specific files
for 20260410")
I am seeing this crash sporadically in Meta fleet across multiple kernel
versions. A full reproducer is available at:
https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh
(The race window is narrow. To make it easily reproducible, inject a
msleep(100) between css_put() and blkcg_unpin_online() in
cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the
reproducer triggers the splat reliably in less than a second.)
Fix this by moving blkcg_unpin_online() before css_put(), so the
cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online()
accesses it.
Severity ?
7.8 (High)
Assigner
References
Impacted products
| Vendor | Product | Version | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux |
Affected:
59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 115a5266749dcde7fe4127e8623d19c752088f69
(git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < dfc8292a1d6782c76b626315605e0585a5a18447 (git) Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < ea3af09eb87d8f8708c66747fcf1a2762902e839 (git) Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 50879a3c1faf06e661090015d59e2127255cff27 (git) Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 67cb119d32f35e32acd0393bbeb318b2bb1fdafe (git) Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 8f5857be99f1ed1fa80991c72449541f634626ee (git) |
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|
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: blk-cgroup: fix use-after-free in cgwb_release_workfn()\n\ncgwb_release_workfn() calls css_put(wb-\u003eblkcg_css) and then later accesses\nwb-\u003eblkcg_css again via blkcg_unpin_online(). If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn -\u003e\nblkcg_css_free -\u003e kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg-\u003eonline_pin, resulting in a use-after-free:\n\n BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\n Workqueue: cgwb_release cgwb_release_workfn\n Call Trace:\n \u003cTASK\u003e\n blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n cgwb_release_workfn (mm/backing-dev.c:629)\n process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\n\n Freed by task 1016:\n kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\n css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\n process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\n\n** Stack based on commit 66672af7a095 (\"Add linux-next specific files\nfor 20260410\")\n\nI am seeing this crash sporadically in Meta fleet across multiple kernel\nversions. A full reproducer is available at:\nhttps://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh\n\n(The race window is narrow. To make it easily reproducible, inject a\nmsleep(100) between css_put() and blkcg_unpin_online() in\ncgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the\nreproducer triggers the splat reliably in less than a second.)\n\nFix this by moving blkcg_unpin_online() before css_put(), so the\ncgwb\u0027s CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."
}
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If css_put() drops the last\\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn -\u003e\\nblkcg_css_free -\u003e kfree) before blkcg_unpin_online() dereferences the\\npointer to access blkcg-\u003eonline_pin, resulting in a use-after-free:\\n\\n BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\\n Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\\n Workqueue: cgwb_release cgwb_release_workfn\\n Call Trace:\\n \u003cTASK\u003e\\n blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\\n cgwb_release_workfn (mm/backing-dev.c:629)\\n process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\\n\\n Freed by task 1016:\\n kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\\n css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\\n process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\\n\\n** Stack based on commit 66672af7a095 (\\\"Add linux-next specific files\\nfor 20260410\\\")\\n\\nI am seeing this crash sporadically in Meta fleet across multiple kernel\\nversions. 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}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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