Tracker / CVE-2026-31555
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.
Affected products and versions
| linux | linux_kernel |
|---|---|
| linux | linux_kernel · 4.14.158 → 4.15 |
| linux | linux_kernel · 4.19.172 → 4.20 |
| linux | linux_kernel · 4.4.255 → 4.5 |
| linux | linux_kernel · 4.9.255 → 4.10 |
| linux | linux_kernel · 5.11 → 5.15.203 |
| linux | linux_kernel · 5.16 → 6.1.168 |
| linux | linux_kernel · 5.4.1 → 5.5 |
| linux | linux_kernel · 5.5.1 → 5.10.253 |
| linux | linux_kernel · 6.13 → 6.18.21 |
| linux | linux_kernel · 6.19 → 6.19.11 |
| linux | linux_kernel · 6.2 → 6.6.131 |
| linux | linux_kernel · 6.7 → 6.12.80 |