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CVE-2026-31555

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

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 4.5, 4.10, 4.15, 4.20, 5.5, and 7 more
None on Exploit-DB, Metasploit or GitHub

Summary

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.

Timeline

  1. CVE published
  2. Record last updated

Affected versions

  • Linux Linux

    From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in e7824ec168d2ac883a213cd1f4d6cc0816002a85; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 5e8e06bf8909e79b4acd950cf578cfc2f10bbefa; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in de7c0c04ad868f2cee6671b11c0a6d20421af1da; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 7475dfad10a05a5bfadebf5f2499bd61b19ed293; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 92e47ad03e03dbb5515bdf06444bf6b1e147310d; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 71112e62807d1925dc3ae6188b11f8cfc85aec23; From 3ef240eaff36b8119ac9e2ea17cbf41179c930ba · fixed in 210d36d892de5195e6766c45519dfb1e65f3eb83; From 4.4.255 · fixed in 4.5; From 4.9.255 · fixed in 4.10; From 4.14.158 · fixed in 4.15; From 4.19.172 · fixed in 4.20; From 5.4.1 · fixed in 5.5

  • Linux Linux

    5.5

  • KernelLinux

    From 5.5.0 · fixed in 5.10.253; From 5.11.0 · fixed in 5.15.203; From 5.16.0 · fixed in 6.1.168; From 6.2.0 · fixed in 6.6.131; From 6.7.0 · fixed in 6.12.80; From 6.13.0 · fixed in 6.18.21; From 6.19.0 · fixed in 6.19.11

References 8

git.kernel.org