linux-kernel - [PATCH 4.9 48/53] futex: Fix incorrect should_fail

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Message-Id: <20210329075609.096873496@linuxfoundation.org>
Date:   Mon, 29 Mar 2021 09:58:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mateusz Nosek <mateusznosek0@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>
Subject: [PATCH 4.9 48/53] futex: Fix incorrect should_fail_futex() handling

From: Mateusz Nosek <mateusznosek0@...il.com>

commit 921c7ebd1337d1a46783d7e15a850e12aed2eaa0 upstream.

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
Signed-off-by: Sasha Levin <sashal@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/futex.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1605,8 +1605,10 @@ static int wake_futex_pi(u32 __user *uad
 	 */
 	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)) {