[PATCH 4.14 016/125] futex: Fix incorrect should_fail_futex() handling

Greg Kroah-Hartman
2020-11-03T21:18:50Z

From: Mateusz Nosek <mateusznosek0@gmail.com>

[ Upstream commit 921c7ebd1337d1a46783d7e15a850e12aed2eaa0 ]

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@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200927000858.24219-1-mateusznosek0@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/futex.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 2921ebaa14676..8f0e62c59a55b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1595,8 +1595,10 @@ 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)) {
--
2.27.0