linux-kernel - [tip: locking/urgent] futex: Fix incorrect should_fail

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Date:   Wed, 28 Oct 2020 14:53:51 -0000
From:   "tip-bot2 for Mateusz Nosek" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Mateusz Nosek <mateusznosek0@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/urgent] futex: Fix incorrect should_fail_futex() handling

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

Commit-ID:     921c7ebd1337d1a46783d7e15a850e12aed2eaa0
Gitweb:        https://git.kernel.org/tip/921c7ebd1337d1a46783d7e15a850e12aed2eaa0
Author:        Mateusz Nosek <mateusznosek0@...il.com>
AuthorDate:    Sun, 27 Sep 2020 02:08:58 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 28 Oct 2020 15:48:51 +01:00

futex: Fix incorrect should_fail_futex() handling

If should_futex_fail() returns true in futex_wake_pi(), then the 'ret'
variable is set to -EFAULT and then immediately overwritten. So the failure
injection is non-functional.

Fix it by actually leaving the function and returning -EFAULT.

The Fixes tag is kinda blury because the initial commit which introduced
failure injection was already sloppy, but the below mentioned commit broke
it completely.

[ tglx: Massaged changelog ]

Fixes: 6b4f4bc9cb22 ("locking/futex: Allow low-level atomic operations to return -EAGAIN")
Signed-off-by: Mateusz Nosek <mateusznosek0@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/20200927000858.24219-1-mateusznosek0@gmail.com

---
 kernel/futex.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index a587669..39681bf 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1502,8 +1502,10 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
 	 */
 	newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
 
-	if (unlikely(should_fail_futex(true)))
+	if (unlikely(should_fail_futex(true))) {
 		ret = -EFAULT;
+		goto out_unlock;
+	}
 
 	ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
 	if (!ret && (curval != uval)) {