CVE-2026-31555

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.

• linux linux kernel (>= 4.4.255 < 4.5) • linux linux kernel (>= 4.9.255 < 4.10) • linux linux kernel (>= 4.14.158 < 4.15) • linux linux kernel (>= 4.19.172 < 4.20) • linux linux kernel (>= 5.4.1 < 5.5) • linux linux kernel (>= 5.5.1 < 5.10.253) • linux linux kernel (>= 5.11 < 5.15.203) • linux linux kernel (>= 5.16 < 6.1.168) • linux linux kernel (>= 6.2 < 6.6.131) • linux linux kernel (>= 6.7 < 6.12.80) • linux linux kernel (>= 6.13 < 6.18.21) • linux linux kernel (>= 6.19 < 6.19.11) • linux linux kernel 5.5 • linux linux kernel 7.0