linux-kernel - [tip: locking/core] futex: Reorder sanity checks in futex

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Date:   Tue, 17 Aug 2021 20:14:01 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] futex: Reorder sanity checks in futex_requeue()

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     d69cba5c719b0c551f6380ec5da4ed8c20a3815a
Gitweb:        https://git.kernel.org/tip/d69cba5c719b0c551f6380ec5da4ed8c20a3815a
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Sun, 15 Aug 2021 23:29:15 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 17 Aug 2021 19:05:54 +02:00

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20210815211305.581789253@linutronix.de
---
 kernel/futex.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 8d8bad5..a5232f6 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1934,13 +1934,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
 			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 *uaddr1, unsigned int flags,
 		 */
 		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: