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 1CC8B435ED0; Tue, 21 Jul 2026 07:55:10 +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=1784620512; cv=none; b=bBr0VNuA5j6R+6Biy7FFDstVKBhrLoyrG5S09AcFhzqinJ8UmA6YBFEswyPPxNZemZX2ku2fQLwawc4WmSadxr62fK+MBss1cNA83ZWQkgX/whUiG7hb7oNooA+1UswFA+dhV4ctW5cNK6Y4xPIEmntm+xaw7X7DGd5EVXq/mZw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784620512; c=relaxed/simple; bh=LEyffTHmMPKmvxE1F8/aui1m0CrC9UpAk6uIZV8NrRM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=c689aJW5qtTXJBpgPOISuNAW8NBDRM7Tj5Q/PKbRnAx67gBX+d1RAYcwwlO5lXEdZ27CTbwmYqG9JkqI2W/OC26z5vIki1paGouaNL/XFWta84BfqUPw/r3QIbVucUjfgbOmnE5FUZgk/zjdsf5I/pQFgAZryznexvMCpVFD8cQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lCeU/yxw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lCeU/yxw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D36261F000E9; Tue, 21 Jul 2026 07:55:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784620510; bh=b7vYQhguU740syKNSWYQ0h3PqXT9T6A3fFsJKPmQ218=; h=From:To:Cc:Subject:Date; b=lCeU/yxwsO6vP0Bhs//tpwFPhJlyk1tFMBJDQSO2JKYCbYVphdHb34KgjdiKccjpR 74C4nFRIPdwMdbu9XF4EjcnX9bgRAbeUkSJR5aCRNdSbfhhDpv3+9GO1Mlq+OD56CV msCZJA/M22K2PE8wqNmRKYMlOpAVF8q7CvkVNFEB+83M68TanntEeY+tyUp3exLao8 jpvaaRc4TrRM3rkZFS7MWkDgvmBrAm8hxlYlOEND0Z90kIn63NOH1LLOwJu7d8wHUG 9midjPYX09kGziQ8EEFW4STUhaHflo/z5fFASyI/wEiU28qn7neuu0O2rvGklPuHLj dh18RM3oMyDEQ== From: Lee Jones To: lee@kernel.org, Peter Zijlstra , Ingo Molnar , Will Deacon , Steven Rostedt , Lai Jiangshan , Thomas Gleixner , Keenan Dong , linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org, Yuan Tan , Yifan Wu , Juefei Pu , Xin Liu , Greg Kroah-Hartman Subject: [STABLE v5.10 1/2] rtmutex: Use waiter::task instead of current in remove_waiter() Date: Tue, 21 Jul 2026 08:54:53 +0100 Message-ID: <20260721075459.1970132-1-lee@kernel.org> X-Mailer: git-send-email 2.55.0.229.g6434b31f56-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 (cherry picked from commit d8cce4773c2b23d819baf5abedc62f7b430e8745) [Lee: Backported to linux-5.10.y from linux-6.1.y] Signed-off-by: Lee Jones --- 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 c6a2dafd4a3b..2ab2d6cce004 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1061,20 +1061,23 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, * * Must be called with lock->wait_lock held and interrupts disabled. I must * have just failed to try_to_take_rt_mutex(). + * + * When invoked from rt_mutex_start_proxy_lock() waiter::task != current ! */ static void remove_waiter(struct rt_mutex *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 *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 @@ -1110,7 +1113,7 @@ static void remove_waiter(struct rt_mutex *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); } -- 2.55.0.229.g6434b31f56-goog