From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 611493B9930; Tue, 21 Jul 2026 21:55:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784670901; cv=none; b=DtjrdMuV8ee26jIroaczAnVmWuhqUbDtlduSdxB9YWorHjNUKgICFuKQqJrDH+KVN7T4M6+U6gXJ9MrVEmW877z8gA9OLiO/qWzIWCn3g3a5HdexKP9LSJ98lUchRpAZUi15wEAZBJFaEl7Ab+R2DxG/0GAoWl1TK0vCretheno= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784670901; c=relaxed/simple; bh=o+O1VidZy53TnaAJHnrXL2MS7bARXHPHDcdY3+frj5Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CzOup/oSnFZexzC7n99xi7YCwq0L14jky2LErBqzkg6iy6AtEbj7Yf2M3/16zYrMWFMAyQC6ZwOVT0TxYtrJg8FLSMqu3UJ7eqUjk1M/5i5EsjVZnB0SIyAs7pGXaD4ESgc3tiUamsGsMhPR7ambMvR2REOIliwcsDhbaEIt5jk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=nDHxeJTv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nDHxeJTv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE7C11F000E9; Tue, 21 Jul 2026 21:54:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784670900; bh=CUhkG8Rf81oZ0vw+4CEhaWmWZlrK8cncgUQ+14+JhpQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nDHxeJTvVHbpUy4dJxMSnrOfCaRfrq9OyPvCMlivtq3XTfFXNCgCeogd552DOv0n0 mbxlry1+2AjB4T7QyybfJE7ASaYgJnPQNVPWJ2FE9f4BY+YMAzHQt9L6Qpu29jt1ft r6NzWzHRJyDLC/Xm2UQ0SXUA/JUrzgmywq+8IxOg= 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 , Sasha Levin Subject: [PATCH 5.15 044/843] rtmutex: Use waiter::task instead of current in remove_waiter() Date: Tue, 21 Jul 2026 17:14:39 +0200 Message-ID: <20260721152406.971147013@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152405.946368001@linuxfoundation.org> References: <20260721152405.946368001@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Keenan Dong [ Upstream commit 3bfdc63936dd4773109b7b8c280c0f3b5ae7d349 ] 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: Sasha Levin --- kernel/locking/rtmutex.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index cf72ef77bfe75a..f79c9286c7c0c1 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1500,20 +1500,23 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, * * 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); + raw_spin_lock(&waiter_task->pi_lock); rt_mutex_dequeue(lock, waiter); - current->pi_blocked_on = NULL; - raw_spin_unlock(¤t->pi_lock); + waiter_task->pi_blocked_on = NULL; + raw_spin_unlock(&waiter_task->pi_lock); /* * Only update priority if the waiter was the highest priority @@ -1549,7 +1552,7 @@ static void __sched remove_waiter(struct rt_mutex_base *lock, 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); } -- 2.53.0