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 7F18D328255; Mon, 13 Apr 2026 16:57:27 +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=1776099447; cv=none; b=mWFSfey2CFZcHzi1j6CjOYotYmXOj4G/z1ZhSu7aDV9EpjmRh/YVoAWe8TF7Qv9htMdd+0FUYBUGGG0Q1hG/c8f4iQJhhQAo+T3jZqOc1acCJhrBaaUkazXhQryGrswnsWc3eLgVE2Ygy6v67PkpwaH8QIpG1WsjEMRCIIQOauk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776099447; c=relaxed/simple; bh=27rknvOs6r6Ei4ETSGt6AC2D0LqTfMmu8QGxEpoNEBI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=huQ/idsInCZxu8qQNoOnjgDiLUNTcoj5vhV2/P4qxWU8O0SwRIfBAMkenpw2hhBVCdS+CrrExb8H6odXzWXFctMhPc+NPhotdJ8SOGIFULJeuUU+zsrwlvoc2V0NQDr8fB9gG3VzwwnFSRA0BPiDI98R+3FrQfcwVDsysriOwqk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Iq73lOT9; 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="Iq73lOT9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 142AFC2BCAF; Mon, 13 Apr 2026 16:57:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776099447; bh=27rknvOs6r6Ei4ETSGt6AC2D0LqTfMmu8QGxEpoNEBI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Iq73lOT9HsZg/ad/p90RKxkvtkyBNA047lxEpzomFisd7ynxmxEC1MtAlXNekvwEU g2Z2pRs6rmrFLcQCSxZbn0mI4OiUjlqVSsrNR9BWTFuRi3cnLYK4Pp9gb/FkCCA9fC I4vwrSBj+ThUdF5SmAG+Th9M5drx0fWmaU0w4srU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Davidlohr Bueso , Thomas Gleixner Subject: [PATCH 5.10 316/491] futex: Clear stale exiting pointer in futex_lock_pi() retry path Date: Mon, 13 Apr 2026 17:59:21 +0200 Message-ID: <20260413155830.868557573@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260413155819.042779211@linuxfoundation.org> References: <20260413155819.042779211@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-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 @@ -2785,9 +2785,9 @@ 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; @@ -2800,6 +2800,7 @@ static int futex_lock_pi(u32 __user *uad to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0); retry: + exiting = NULL; ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); if (unlikely(ret != 0)) goto out;