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CVE PROGRAM SOURCE RECORDUnscored

CVE-2026-31555

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

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Status
Published
Published
Updated
Assigning organization
Linux

Description

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 33095ae3bdde5e5c264d7e88a2f3e7703a26c7aaaffected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < e7824ec168d2ac883a213cd1f4d6cc0816002a85affected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 5e8e06bf8909e79b4acd950cf578cfc2f10bbefaaffected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < de7c0c04ad868f2cee6671b11c0a6d20421af1daaffected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 7475dfad10a05a5bfadebf5f2499bd61b19ed293affected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 92e47ad03e03dbb5515bdf06444bf6b1e147310daffected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 71112e62807d1925dc3ae6188b11f8cfc85aec23affected
  • 3ef240eaff36b8119ac9e2ea17cbf41179c930ba to < 210d36d892de5195e6766c45519dfb1e65f3eb83affected
  • f2a9957e5c08b1b1caacd18a3dc4c0a1bdb7b463affected
  • cf16e42709aa86aa3e37f3acc3d13d5715d90096affected
  • 61fa9f167caaa73d0a7c88f498eceeb12c6fa3dbaffected
  • 7874eee0130adf9bee28e8720bb5dd051089def3affected
  • fc3b55ef2c840bb2746b2d8121a0788de84f7facaffected
  • 4.4.255 to < 4.5affected
  • 4.9.255 to < 4.10affected
  • 4.14.158 to < 4.15affected
  • 4.19.172 to < 4.20affected
  • 5.4.1 to < 5.5affected

Linux Linux

Default version status: affected

  • 5.5affected
  • 0 to < 5.5unaffected
  • 5.10.253 to ≤ 5.10.*unaffected
  • 5.15.203 to ≤ 5.15.*unaffected
  • 6.1.168 to ≤ 6.1.*unaffected
  • 6.6.131 to ≤ 6.6.*unaffected
  • 6.12.80 to ≤ 6.12.*unaffected
  • 6.18.21 to ≤ 6.18.*unaffected
  • 6.19.11 to ≤ 6.19.*unaffected
  • 7.0 to ≤ *unaffected

References