From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C2E4F2D0C7E; Mon, 13 Apr 2026 16:35:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776098112; cv=none; b=t4X5rfdNDRbJOnC4Drr+WSUPER5AxnitoMEkrZu4KxkuzuIdo1Wj74oexFowFUKxI9XSFCPsK7bWS7iw3V12ojusHRj7GEaFHuTFNlC3ckmHLYX3aIlbDGtTPF0wF+Mk+W8/UssIRr12Egf0bzm2VFp8l3EWRDtdjwFyXgQO2bs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776098112; c=relaxed/simple; bh=sQg0C5L+W8d8kUDYpbl2FEvzzYHnVRPdbRFgaw2dTT8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jl/mJYdaQwg2cSiB5o5q+FzI6Wjohrtj3lRhOMRawtu2MAvXtyH8f5anPFmA2oJC2F2mMCSsTJS+oGcwUDmVBmN5LgDXzlPsRfA+LaAWO5VOK8MZJVjCWwOR32yT9GNXxgiiS7I89r8g3gxCfNl8CogSPK+5cdNNk7v0tYG6IxQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kxB3kqOF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kxB3kqOF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E7ABC2BCAF; Mon, 13 Apr 2026 16:35:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776098112; bh=sQg0C5L+W8d8kUDYpbl2FEvzzYHnVRPdbRFgaw2dTT8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kxB3kqOFL79UrqDLWrKZ5hht/2HvIvLaVbwj3maw3MMD3SPYfqPM83a31/nEyFvf0 Oa0ApG2tKlwt3A69aHTnWN99Rgc+GVaMQxKI3XvRhaJQ5r0Y4YAaHLBQ8R2H+uhvX4 5Wkof6PKm/nWQmV7Gzi5aHIZzrT4iIjn2/kY1KP0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Davidlohr Bueso , Thomas Gleixner Subject: [PATCH 5.15 397/570] futex: Clear stale exiting pointer in futex_lock_pi() retry path Date: Mon, 13 Apr 2026 17:58:48 +0200 Message-ID: <20260413155845.344311615@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260413155830.386096114@linuxfoundation.org> References: <20260413155830.386096114@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Davidlohr Bueso 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 Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260326001759.4129680-1-dave@stgolabs.net Signed-off-by: Greg Kroah-Hartman --- kernel/futex/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -3029,9 +3029,9 @@ static int futex_lock_pi(u32 __user *uad 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; @@ -3044,6 +3044,7 @@ static int futex_lock_pi(u32 __user *uad 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;