linux-kernel - [patch V5 64/72] futex: Reorder sanity checks in futex

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Message-ID: <20210815211305.581789253@linutronix.de>
Date:   Sun, 15 Aug 2021 23:29:15 +0200 (CEST)
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>,
        Mike Galbraith <efault@....de>
Subject: [patch V5 64/72] futex: Reorder sanity checks in futex_requeue()

No point in allocating memory when the input parameters are bogus. Validate
all parameters before proceeding.

Suggested-by: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V4: New patch
---
 kernel/futex.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1934,13 +1934,6 @@ static int futex_requeue(u32 __user *uad
 			return -EINVAL;
 
 		/*
-		 * requeue_pi requires a pi_state, try to allocate it now
-		 * without any locks in case it fails.
-		 */
-		if (refill_pi_state_cache())
-			return -ENOMEM;
-
-		/*
 		 * futex_requeue() allows the caller to define the number
 		 * of waiters to wake up via the @nr_wake argument. With
 		 * REQUEUE_PI waking up more than one waiter is creating
@@ -1963,6 +1956,13 @@ static int futex_requeue(u32 __user *uad
 		 */
 		if (nr_wake != 1)
 			return -EINVAL;
+
+		/*
+		 * requeue_pi requires a pi_state, try to allocate it now
+		 * without any locks in case it fails.
+		 */
+		if (refill_pi_state_cache())
+			return -ENOMEM;
 	}
 
 retry: