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 9D9E63DEAD3; Mon, 4 May 2026 14:26:35 +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=1777904795; cv=none; b=bZAxzUcxHuReCBmZ8FXxV4RxEc2nceKw12qmZiV49hBQSlzBuXHmVDqGxTtUDe3IR17larvLJYMa9kp8j54jya122jBe5BLZEtyU5IIO+HqBcXTKlZP9dj/f+5gODFJdfQDvxAZoGpUDZK4aIWh61p/yRIWSb26WWMFFa6QApYg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777904795; c=relaxed/simple; bh=jXWpQgccxca/1JZ37xyH/8yD+O8bejF4wc5nP7K9/xM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=H9cixLHgJhtzySwarHfmGRxUU8s1+0nb5l8wk9PraaKWTs1ZIHhrT+XYFdZLAMtZQDuTEY5GXzXpCYssdsXn/cOKd/pdK+lg4XE/E9cFJMQqYFy4D7mISvz4OPX/2OaBS1pZUCtZDsF4h342j6zii2eRsq4fpcWTg8TfFdL5INE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=QaiwC2DK; 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="QaiwC2DK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 309CEC2BCB8; Mon, 4 May 2026 14:26:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777904795; bh=jXWpQgccxca/1JZ37xyH/8yD+O8bejF4wc5nP7K9/xM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QaiwC2DKaeeyee2rXWFPNzunkj72X7xMtiJPCKCDxJ3AZfiZVXK+nLcw7lVHbiras 3zWZTROfgGxjLe7l4N1ArNrzh1Gj8LnlsW+YahnyUzIp+ojT619+cIT1UjbJLzM5Zf wnuhmH8FPlnvAuFUmHAsQOTzdGRQKKgDx8kF4uow= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yuan Tan , Yifan Wu , Juefei Pu , Xin Liu , Keenan Dong , Thomas Gleixner Subject: [PATCH 6.12 170/215] rtmutex: Use waiter::task instead of current in remove_waiter() Date: Mon, 4 May 2026 15:53:09 +0200 Message-ID: <20260504135136.394866572@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260504135130.169210693@linuxfoundation.org> References: <20260504135130.169210693@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Keenan Dong commit 3bfdc63936dd4773109b7b8c280c0f3b5ae7d349 upstream. remove_waiter() is used by the slowlock paths, but it is also used for proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from futex_requeue(). In the latter case waiter::task is not current, but remove_waiter() operates on current for the dequeue operation. That results in several problems: 1) the rbtree dequeue happens without waiter::task::pi_lock being held 2) the waiter task's pi_blocked_on state is not cleared, which leaves a dangling pointer primed for UAF around. 3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter task Use waiter::task instead of current in all related operations in remove_waiter() to cure those problems. [ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the changelog ] Fixes: 8161239a8bcc ("rtmutex: Simplify PI algorithm and make highest prio task get lock") Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Xin Liu Signed-off-by: Keenan Dong Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- kernel/locking/rtmutex.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1531,20 +1531,23 @@ static bool rtmutex_spin_on_owner(struct * * Must be called with lock->wait_lock held and interrupts disabled. It must * have just failed to try_to_take_rt_mutex(). + * + * When invoked from rt_mutex_start_proxy_lock() waiter::task != current ! */ static void __sched remove_waiter(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter) { bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock)); struct task_struct *owner = rt_mutex_owner(lock); + struct task_struct *waiter_task = waiter->task; struct rt_mutex_base *next_lock; lockdep_assert_held(&lock->wait_lock); - raw_spin_lock(¤t->pi_lock); - rt_mutex_dequeue(lock, waiter); - current->pi_blocked_on = NULL; - raw_spin_unlock(¤t->pi_lock); + scoped_guard(raw_spinlock, &waiter_task->pi_lock) { + rt_mutex_dequeue(lock, waiter); + waiter_task->pi_blocked_on = NULL; + } /* * Only update priority if the waiter was the highest priority @@ -1580,7 +1583,7 @@ static void __sched remove_waiter(struct raw_spin_unlock_irq(&lock->wait_lock); rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock, - next_lock, NULL, current); + next_lock, NULL, waiter_task); raw_spin_lock_irq(&lock->wait_lock); }