CVE-2026-31555 (GCVE-0-2026-31555)
Vulnerability from cvelistv5 – Published: 2026-04-24 14:35 – Updated: 2026-04-24 14:35
VLAI?
Title
futex: Clear stale exiting pointer in futex_lock_pi() retry path
Summary
In the Linux kernel, the following vulnerability has been resolved:
futex: Clear stale exiting pointer in futex_lock_pi() retry path
Fuzzying/stressing futexes triggered:
WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524
When futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY
and stores a refcounted task pointer in 'exiting'.
After wait_for_owner_exiting() consumes that reference, the local pointer
is never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a
different error, the bogus pointer is passed to wait_for_owner_exiting().
CPU0 CPU1 CPU2
futex_lock_pi(uaddr)
// acquires the PI futex
exit()
futex_cleanup_begin()
futex_state = EXITING;
futex_lock_pi(uaddr)
futex_lock_pi_atomic()
attach_to_pi_owner()
// observes EXITING
*exiting = owner; // takes ref
return -EBUSY
wait_for_owner_exiting(-EBUSY, owner)
put_task_struct(); // drops ref
// exiting still points to owner
goto retry;
futex_lock_pi_atomic()
lock_pi_update_atomic()
cmpxchg(uaddr)
*uaddr ^= WAITERS // whatever
// value changed
return -EAGAIN;
wait_for_owner_exiting(-EAGAIN, exiting) // stale
WARN_ON_ONCE(exiting)
Fix this by resetting upon retry, essentially aligning it with requeue_pi.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
| Vendor | Product | Version | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux |
Affected:
3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa
(git)
Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < e7824ec168d2ac883a213cd1f4d6cc0816002a85 (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 5e8e06bf8909e79b4acd950cf578cfc2f10bbefa (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < de7c0c04ad868f2cee6671b11c0a6d20421af1da (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 7475dfad10a05a5bfadebf5f2499bd61b19ed293 (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 92e47ad03e03dbb5515bdf06444bf6b1e147310d (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 71112e62807d1925dc3ae6188b11f8cfc85aec23 (git) Affected: 3ef240eaff36b8119ac9e2ea17cbf41179c930ba , < 210d36d892de5195e6766c45519dfb1e65f3eb83 (git) Affected: f2a9957e5c08b1b1caacd18a3dc4c0a1bdb7b463 (git) Affected: cf16e42709aa86aa3e37f3acc3d13d5715d90096 (git) Affected: 61fa9f167caaa73d0a7c88f498eceeb12c6fa3db (git) Affected: 7874eee0130adf9bee28e8720bb5dd051089def3 (git) Affected: fc3b55ef2c840bb2746b2d8121a0788de84f7fac (git) |
|||||||
|
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{
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"product": "Linux",
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],
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"vendor": "Linux",
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{
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{
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{
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"descriptions": [
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Clear stale exiting pointer in futex_lock_pi() retry path\n\nFuzzying/stressing futexes triggered:\n\n WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524\n\nWhen futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY\nand stores a refcounted task pointer in \u0027exiting\u0027.\n\nAfter wait_for_owner_exiting() consumes that reference, the local pointer\nis never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a\ndifferent error, the bogus pointer is passed to wait_for_owner_exiting().\n\n CPU0\t\t\t CPU1\t\t CPU2\n futex_lock_pi(uaddr)\n // acquires the PI futex\n exit()\n futex_cleanup_begin()\n futex_state = EXITING;\n\t\t\t futex_lock_pi(uaddr)\n\t\t\t futex_lock_pi_atomic()\n\t\t\t\t attach_to_pi_owner()\n\t\t\t\t // observes EXITING\n\t\t\t\t *exiting = owner; // takes ref\n\t\t\t\t return -EBUSY\n\t\t\t wait_for_owner_exiting(-EBUSY, owner)\n\t\t\t\t put_task_struct(); // drops ref\n\t\t\t // exiting still points to owner\n\t\t\t goto retry;\n\t\t\t futex_lock_pi_atomic()\n\t\t\t\t lock_pi_update_atomic()\n\t\t\t\t cmpxchg(uaddr)\n\t\t\t\t\t*uaddr ^= WAITERS // whatever\n\t\t\t\t // value changed\n\t\t\t\t return -EAGAIN;\n\t\t\t wait_for_owner_exiting(-EAGAIN, exiting) // stale\n\t\t\t\t WARN_ON_ONCE(exiting)\n\nFix this by resetting upon retry, essentially aligning it with requeue_pi."
}
],
"providerMetadata": {
"dateUpdated": "2026-04-24T14:35:39.211Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa"
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{
"url": "https://git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85"
},
{
"url": "https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa"
},
{
"url": "https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da"
},
{
"url": "https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293"
},
{
"url": "https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d"
},
{
"url": "https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23"
},
{
"url": "https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83"
}
],
"title": "futex: Clear stale exiting pointer in futex_lock_pi() retry path",
"x_generator": {
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}
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"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-31555",
"datePublished": "2026-04-24T14:35:39.211Z",
"dateReserved": "2026-03-09T15:48:24.115Z",
"dateUpdated": "2026-04-24T14:35:39.211Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-31555",
"date": "2026-04-26",
"epss": "0.00024",
"percentile": "0.06793"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-31555\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-04-24T15:16:29.837\",\"lastModified\":\"2026-04-24T17:51:40.810\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nfutex: Clear stale exiting pointer in futex_lock_pi() retry path\\n\\nFuzzying/stressing futexes triggered:\\n\\n WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524\\n\\nWhen futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY\\nand stores a refcounted task pointer in \u0027exiting\u0027.\\n\\nAfter wait_for_owner_exiting() consumes that reference, the local pointer\\nis never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a\\ndifferent error, the bogus pointer is passed to wait_for_owner_exiting().\\n\\n CPU0\\t\\t\\t CPU1\\t\\t CPU2\\n futex_lock_pi(uaddr)\\n // acquires the PI futex\\n exit()\\n futex_cleanup_begin()\\n futex_state = EXITING;\\n\\t\\t\\t futex_lock_pi(uaddr)\\n\\t\\t\\t futex_lock_pi_atomic()\\n\\t\\t\\t\\t attach_to_pi_owner()\\n\\t\\t\\t\\t // observes EXITING\\n\\t\\t\\t\\t *exiting = owner; // takes ref\\n\\t\\t\\t\\t return -EBUSY\\n\\t\\t\\t wait_for_owner_exiting(-EBUSY, owner)\\n\\t\\t\\t\\t put_task_struct(); // drops ref\\n\\t\\t\\t // exiting still points to owner\\n\\t\\t\\t goto retry;\\n\\t\\t\\t futex_lock_pi_atomic()\\n\\t\\t\\t\\t lock_pi_update_atomic()\\n\\t\\t\\t\\t cmpxchg(uaddr)\\n\\t\\t\\t\\t\\t*uaddr ^= WAITERS // whatever\\n\\t\\t\\t\\t // value changed\\n\\t\\t\\t\\t return -EAGAIN;\\n\\t\\t\\t wait_for_owner_exiting(-EAGAIN, exiting) // stale\\n\\t\\t\\t\\t WARN_ON_ONCE(exiting)\\n\\nFix this by resetting upon retry, essentially aligning it with requeue_pi.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
}
}
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Sightings
| Author | Source | Type | Date |
|---|
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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