CVE-2026-31555Medium· 5.5▾ SunlitIn 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+…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 30.3 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.1%
— → 5.5
none → medium
0.1% → 0.2%
Last analysed / modified upstream
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_kernel >= 4.4.255, < 4.5linux_kernel >= 4.9.255, < 4.10linux_kernel >= 4.14.158, < 4.15linux_kernel >= 4.19.172, < 4.20linux_kernel >= 5.4.1, < 5.5linux_kernel >= 5.5.1, < 5.10.253linux_kernel >= 5.11, < 5.15.203linux_kernel >= 5.16, < 6.1.168linux_kernel >= 6.2, < 6.6.131linux_kernel >= 6.7, < 6.12.80linux_kernel >= 6.13, < 6.18.21linux_kernel >= 6.19, < 6.19.11linux_kernel = 5.5linux_kernel = 7.0Upgrade past the affected range:
linux_kernel 6.19.11Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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