[patch V3 54/64] futex: Validate waiter correctly in futex_proxy_trylock_atomic()

[Thomas Gleixner]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
 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;