futex: Clear stale exiting pointer in futex_lock_pi() retry path

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Summary

CVECVE-2026-31555
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-24 15:16:29 UTC
Updated2026-07-14 13:18:45 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.000240000 probability, percentile 0.067850000 (date 2026-04-27)

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba e7824ec168d2ac883a213cd1f4d6cc0816002a85 git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 5e8e06bf8909e79b4acd950cf578cfc2f10bbefa git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba de7c0c04ad868f2cee6671b11c0a6d20421af1da git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 7475dfad10a05a5bfadebf5f2499bd61b19ed293 git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 92e47ad03e03dbb5515bdf06444bf6b1e147310d git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 71112e62807d1925dc3ae6188b11f8cfc85aec23 git Not specified
CNA Linux Linux affected 3ef240eaff36b8119ac9e2ea17cbf41179c930ba 210d36d892de5195e6766c45519dfb1e65f3eb83 git Not specified
CNA Linux Linux affected f2a9957e5c08b1b1caacd18a3dc4c0a1bdb7b463 git Not specified
CNA Linux Linux affected cf16e42709aa86aa3e37f3acc3d13d5715d90096 git Not specified
CNA Linux Linux affected 61fa9f167caaa73d0a7c88f498eceeb12c6fa3db git Not specified
CNA Linux Linux affected 7874eee0130adf9bee28e8720bb5dd051089def3 git Not specified
CNA Linux Linux affected fc3b55ef2c840bb2746b2d8121a0788de84f7fac git Not specified
CNA Linux Linux affected 4.4.255 4.5 semver Not specified
CNA Linux Linux affected 4.9.255 4.10 semver Not specified
CNA Linux Linux affected 4.14.158 4.15 semver Not specified
CNA Linux Linux affected 4.19.172 4.20 semver Not specified
CNA Linux Linux affected 5.4.1 5.5 semver Not specified
CNA Linux Linux affected 5.5 Not specified
CNA Linux Linux unaffected 5.5 semver Not specified
CNA Linux Linux unaffected 5.10.253 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.168 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.131 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.80 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.21 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.11 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-082556.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-019113.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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