[patch V4 55/68] futex: Validate waiter correctly in futex_proxy_trylock_atomic()

Thomas Gleixner
2021-08-11T12:25:57Z

The loop in futex_requeue() has a sanity check for the waiter which is
missing in futex_proxy_trylock_atomic(). In theory the key2 check is
sufficient, but futexes are cursed so add it for completeness and paranoia
sake.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/futex.c | 7 +++++++
1 file changed, 7 insertions(+)
---
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1879,6 +1879,13 @@ futex_proxy_trylock_atomic(u32 __user *p
if (!top_waiter)
return 0;

+ /*
+ * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
+ * and waiting on the 'waitqueue' futex which is always !PI.
+ */
+ if (!top_waiter->rt_waiter || top_waiter->pi_state)
+ ret = -EINVAL;
+
/* Ensure we requeue to the expected futex. */
if (!match_futex(top_waiter->requeue_pi_key, key2))
return -EINVAL;