CVE-2026-43439 (GCVE-0-2026-43439)
Vulnerability from cvelistv5
Published
2026-05-08 14:22
Modified
2026-05-23 16:07
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
cgroup: fix race between task migration and iteration
When a task is migrated out of a css_set, cgroup_migrate_add_task()
first moves it from cset->tasks to cset->mg_tasks via:
list_move_tail(&task->cg_list, &cset->mg_tasks);
If a css_task_iter currently has it->task_pos pointing to this task,
css_set_move_task() calls css_task_iter_skip() to keep the iterator
valid. However, since the task has already been moved to ->mg_tasks,
the iterator is advanced relative to the mg_tasks list instead of the
original tasks list. As a result, remaining tasks on cset->tasks, as
well as tasks queued on cset->mg_tasks, can be skipped by iteration.
Fix this by calling css_set_skip_task_iters() before unlinking
task->cg_list from cset->tasks. This advances all active iterators to
the next task on cset->tasks, so iteration continues correctly even
when a task is concurrently being migrated.
This race is hard to hit in practice without instrumentation, but it
can be reproduced by artificially slowing down cgroup_procs_show().
For example, on an Android device a temporary
/sys/kernel/cgroup/cgroup_test knob can be added to inject a delay
into cgroup_procs_show(), and then:
1) Spawn three long-running tasks (PIDs 101, 102, 103).
2) Create a test cgroup and move the tasks into it.
3) Enable a large delay via /sys/kernel/cgroup/cgroup_test.
4) In one shell, read cgroup.procs from the test cgroup.
5) Within the delay window, in another shell migrate PID 102 by
writing it to a different cgroup.procs file.
Under this setup, cgroup.procs can intermittently show only PID 101
while skipping PID 103. Once the migration completes, reading the
file again shows all tasks as expected.
Note that this change does not allow removing the existing
css_set_skip_task_iters() call in css_set_move_task(). The new call
in cgroup_migrate_add_task() only handles iterators that are racing
with migration while the task is still on cset->tasks. Iterators may
also start after the task has been moved to cset->mg_tasks. If we
dropped css_set_skip_task_iters() from css_set_move_task(), such
iterators could keep task_pos pointing to a migrating task, causing
css_task_iter_advance() to malfunction on the destination css_set,
up to and including crashes or infinite loops.
The race window between migration and iteration is very small, and
css_task_iter is not on a hot path. In the worst case, when an
iterator is positioned on the first thread of the migrating process,
cgroup_migrate_add_task() may have to skip multiple tasks via
css_set_skip_task_iters(). However, this only happens when migration
and iteration actually race, so the performance impact is negligible
compared to the correctness fix provided here.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b636fd38dc40113f853337a7d2a6885ad23b8811 Version: b0af004fd58ded5f898630db008c5b824c27d7db Version: 370b9e6399da09fe10005fe455878b356de7b85f Version: 4.14.138 ≤ Version: 4.19.66 ≤ |
||
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncgroup: fix race between task migration and iteration\n\nWhen a task is migrated out of a css_set, cgroup_migrate_add_task()\nfirst moves it from cset-\u003etasks to cset-\u003emg_tasks via:\n\n list_move_tail(\u0026task-\u003ecg_list, \u0026cset-\u003emg_tasks);\n\nIf a css_task_iter currently has it-\u003etask_pos pointing to this task,\ncss_set_move_task() calls css_task_iter_skip() to keep the iterator\nvalid. However, since the task has already been moved to -\u003emg_tasks,\nthe iterator is advanced relative to the mg_tasks list instead of the\noriginal tasks list. As a result, remaining tasks on cset-\u003etasks, as\nwell as tasks queued on cset-\u003emg_tasks, can be skipped by iteration.\n\nFix this by calling css_set_skip_task_iters() before unlinking\ntask-\u003ecg_list from cset-\u003etasks. This advances all active iterators to\nthe next task on cset-\u003etasks, so iteration continues correctly even\nwhen a task is concurrently being migrated.\n\nThis race is hard to hit in practice without instrumentation, but it\ncan be reproduced by artificially slowing down cgroup_procs_show().\nFor example, on an Android device a temporary\n/sys/kernel/cgroup/cgroup_test knob can be added to inject a delay\ninto cgroup_procs_show(), and then:\n\n 1) Spawn three long-running tasks (PIDs 101, 102, 103).\n 2) Create a test cgroup and move the tasks into it.\n 3) Enable a large delay via /sys/kernel/cgroup/cgroup_test.\n 4) In one shell, read cgroup.procs from the test cgroup.\n 5) Within the delay window, in another shell migrate PID 102 by\n writing it to a different cgroup.procs file.\n\nUnder this setup, cgroup.procs can intermittently show only PID 101\nwhile skipping PID 103. Once the migration completes, reading the\nfile again shows all tasks as expected.\n\nNote that this change does not allow removing the existing\ncss_set_skip_task_iters() call in css_set_move_task(). The new call\nin cgroup_migrate_add_task() only handles iterators that are racing\nwith migration while the task is still on cset-\u003etasks. Iterators may\nalso start after the task has been moved to cset-\u003emg_tasks. If we\ndropped css_set_skip_task_iters() from css_set_move_task(), such\niterators could keep task_pos pointing to a migrating task, causing\ncss_task_iter_advance() to malfunction on the destination css_set,\nup to and including crashes or infinite loops.\n\nThe race window between migration and iteration is very small, and\ncss_task_iter is not on a hot path. In the worst case, when an\niterator is positioned on the first thread of the migrating process,\ncgroup_migrate_add_task() may have to skip multiple tasks via\ncss_set_skip_task_iters(). However, this only happens when migration\nand iteration actually race, so the performance impact is negligible\ncompared to the correctness fix provided here."
}
],
"providerMetadata": {
"dateUpdated": "2026-05-23T16:07:00.399Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/7c85debc35e6d131bd29c64f2ae78c6ede0e55c4"
},
{
"url": "https://git.kernel.org/stable/c/3b95abab7369235a37b15eaec6e1a0b443bba7c7"
},
{
"url": "https://git.kernel.org/stable/c/4a9654a2b46cfdaae287fb8995f536245635e467"
},
{
"url": "https://git.kernel.org/stable/c/3dfd1328c05234e8d8fa61948b2ba82680594988"
},
{
"url": "https://git.kernel.org/stable/c/9cca530c7cc1b3e02cb8fa7f80060dd4b38562ce"
},
{
"url": "https://git.kernel.org/stable/c/86ceaccfdfa16dad05addb33dc206e03589bcfd1"
},
{
"url": "https://git.kernel.org/stable/c/9dc76f6fc0d28d2382583715bc4ec22f28104845"
},
{
"url": "https://git.kernel.org/stable/c/5ee01f1a7343d6a3547b6802ca2d4cdce0edacb1"
}
],
"title": "cgroup: fix race between task migration and iteration",
"x_generator": {
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}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-43439",
"datePublished": "2026-05-08T14:22:08.626Z",
"dateReserved": "2026-05-01T14:12:56.009Z",
"dateUpdated": "2026-05-23T16:07:00.399Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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