futex: Handle user space corruption gracefully

commit 51246bf upstream. If the owner of a PI futex dies we fix up the pi_state and set pi_state->owner to NULL. When a malicious or just sloppy programmed user space application sets the futex value to 0 e.g. by calling pthread_mutex_init(), then the futex can be acquired again. A new waiter manages to enqueue itself on the pi_state w/o damage, but on unlock the kernel dereferences pi_state->owner and oopses. Prevent this by checking pi_state->owner in the unlock path. If pi_state->owner is not current we know that user space manipulated the futex value. Ignore the mess and return -EINVAL. This catches the above case and also the case where a task hijacks the futex by setting the tid value and then tries to unlock it. Reported-by: Jermome Marchand <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Acked-by: Darren Hart <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
CyanogenMod · Feb 23, 2010 · c03d9d4 · c03d9d4
1 parent 5f6af11
commit c03d9d4
Showing 1 changed file with 7 additions and 0 deletions.
diff --git a/kernel/futex.c b/kernel/futex.c
@@ -758,6 +758,13 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
 	if (!pi_state)
 		return -EINVAL;
 
+	/*
+	 * If current does not own the pi_state then the futex is
+	 * inconsistent and user space fiddled with the futex value.
+	 */
+	if (pi_state->owner != current)
+		return -EINVAL;
+
 	spin_lock(&pi_state->pi_mutex.wait_lock);
 	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);