linux-kernel - [patch 41/50] futex: Validate waiter correctly in futex_proxy_trylock

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Message-Id: <20210713160749.961050050@linutronix.de>
Date:   Tue, 13 Jul 2021 17:11:35 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: [patch 41/50] futex: Validate waiter correctly in
 futex_proxy_trylock_atomic()

From: Thomas Gleixner <tglx@...utronix.de>

The loop in futex_requeue() has a sanity check for the waiter which is
missing in futex_proxy_trylock_atomic(). In theory the key2 check is
sufficient, but futexes are cursed so add it for completness and paranoia
sake.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/futex.c |    4 ++++
 1 file changed, 4 insertions(+)
---
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1879,6 +1879,10 @@ futex_proxy_trylock_atomic(u32 __user *p
 	if (!top_waiter)
 		return 0;
 
+	/* Ensure that this is a waiter sitting in futex_wait_requeue_pi() */
+	if (!top_waiter->rt_waiter || top_waiter->pi_state)
+		ret = -EINVAL;
+
 	/* Ensure we requeue to the expected futex. */
 	if (!match_futex(top_waiter->requeue_pi_key, key2))
 		return -EINVAL;