[patch 41/50] futex: Validate waiter correctly in futex_proxy_trylock_atomic()

From: Thomas Gleixner
Date: Tue Jul 13 2021 - 12:14:51 EST


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 completness and paranoia
sake.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/futex.c | 4 ++++
1 file changed, 4 insertions(+)
---
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1879,6 +1879,10 @@ futex_proxy_trylock_atomic(u32 __user *p
if (!top_waiter)
return 0;

+ /* Ensure that this is a waiter sitting in futex_wait_requeue_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;