linux-kernel - [PATCH RT v2] futex/rtmutex: Cure RT double blocking issue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170511152054.bpgik7etss7umxzq@linutronix.de>
Date:   Thu, 11 May 2017 17:20:54 +0200
From:   Sebastian Sewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Engleder Gerhard <eg@...a.com>
Subject: [PATCH RT v2] futex/rtmutex: Cure RT double blocking issue

RT has a problem when the wait on a futex/rtmutex got interrupted by a
timeout or a signal. task->pi_blocked_on is still set when returning from
rt_mutex_wait_proxy_lock(). The task must acquire the hash bucket lock
after this.

If the hash bucket lock is contended then the
BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
task_blocks_on_rt_mutex() will trigger.

This can be avoided by clearing task->pi_blocked_on in the return path of
rt_mutex_wait_proxy_lock() which removes the task from the boosting chain
of the rtmutex. That's correct because the task is not longer blocked on
it.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reported-by: Engleder Gerhard <eg@...a.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 v1…v2: reset ->pi_blocked_on only in the error case.

 kernel/locking/rtmutex.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 314fc65a35b1..4675f1197f33 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2400,6 +2400,7 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
 			       struct hrtimer_sleeper *to,
 			       struct rt_mutex_waiter *waiter)
 {
+	struct task_struct *tsk = current;
 	int ret;
 
 	raw_spin_lock_irq(&lock->wait_lock);
@@ -2409,6 +2410,24 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
 	/* sleep on the mutex */
 	ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter, NULL);
 
+	/*
+	 * RT has a problem here when the wait got interrupted by a timeout
+	 * or a signal. task->pi_blocked_on is still set. The task must
+	 * acquire the hash bucket lock when returning from this function.
+	 *
+	 * If the hash bucket lock is contended then the
+	 * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
+	 * task_blocks_on_rt_mutex() will trigger. This can be avoided by
+	 * clearing task->pi_blocked_on which removes the task from the
+	 * boosting chain of the rtmutex. That's correct because the task
+	 * is not longer blocked on it.
+	 */
+	if (ret) {
+		raw_spin_lock(&tsk->pi_lock);
+		tsk->pi_blocked_on = NULL;
+		raw_spin_unlock(&tsk->pi_lock);
+	}
+
 	raw_spin_unlock_irq(&lock->wait_lock);
 
 	return ret;
-- 
2.11.0