staging: android: sync: Fix memory corruption in sync_timeline_signal().

The android_fence_release() function checks for active sync points
by calling list_empty() on the list head embedded on the sync
point. However, it is only valid to use list_empty() on nodes that
have been initialized with INIT_LIST_HEAD() or list_del_init().

Because the list entry has likely been removed from the active list
by sync_timeline_signal(), there is a good chance that this
WARN_ON_ONCE() will be hit due to dangling pointers pointing at
freed memory (even though the sync drivers did nothing wrong)
and memory corruption will ensue as the list entry is removed for
a second time, corrupting the active list.

This problem can be reproduced quite easily with CONFIG_DEBUG_LIST=y
and fences with more than one sync point.

Signed-off-by: Alistair Strachan <alistair.strachan@imgtec.com>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Colin Cross <ccross@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index 7bdb62bf6b4054068094590a861f254f76c8b5c8..f83e00c7805130e1ab6dda8d853c2b642b8a4f92 100644 (file)
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -114,7 +114,7 @@ void sync_timeline_signal(struct sync_timeline *obj)
        list_for_each_entry_safe(pt, next, &obj->active_list_head,
                                 active_list) {
                if (fence_is_signaled_locked(&pt->base))
-                       list_del(&pt->active_list);
+                       list_del_init(&pt->active_list);
        }
 
        spin_unlock_irqrestore(&obj->child_list_lock, flags);