From: Davidlohr Bueso <dave@stgolabs.net> stable inclusion from stable-v6.6.131 commit de7c0c04ad868f2cee6671b11c0a6d20421af1da category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14301 CVE: CVE-2026-31555 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 210d36d892de5195e6766c45519dfb1e65f3eb83 upstream. 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. Fixes: 3ef240eaff36 ("futex: Prevent exit livelock") Signed-off-by: Davidlohr Bueso <dave@stgolabs.net> Signed-off-by: Thomas Gleixner <tglx@kernel.org> Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260326001759.4129680-1-dave@stgolabs.net Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Jiacheng Yu <yujiacheng3@huawei.com> --- kernel/futex/pi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c index ce2889f123755..9496084b6dcd8 100644 --- a/kernel/futex/pi.c +++ b/kernel/futex/pi.c @@ -930,9 +930,9 @@ int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked) int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock) { struct hrtimer_sleeper timeout, *to; - struct task_struct *exiting = NULL; struct rt_mutex_waiter rt_waiter; struct futex_hash_bucket *hb; + struct task_struct *exiting; struct futex_q q = futex_q_init; int res, ret; @@ -945,6 +945,7 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl to = futex_setup_timer(time, &timeout, flags, 0); retry: + exiting = NULL; ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); if (unlikely(ret != 0)) goto out; -- 2.43.0