This is a note to let you know that I've just added the patch titled

dma-buf/sw_sync: clean up list before signaling the fence

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: dma-buf-sw_sync-clean-up-list-before-signaling-the-fence.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 3792b7c1a70815fe4e954221c096f9278638fd21 Mon Sep 17 00:00:00 2001

From: Gustavo Padovan gustavo.padovan@collabora.com Date: Sat, 29 Jul 2017 12:22:16 -0300 Subject: dma-buf/sw_sync: clean up list before signaling the fence

From: Gustavo Padovan gustavo.padovan@collabora.com

commit 3792b7c1a70815fe4e954221c096f9278638fd21 upstream.

If userspace already dropped its own reference by closing the sw_sync fence fd we might end up in a deadlock where dma_fence_is_signaled_locked() will trigger the release of the fence and thus try to hold the lock to remove the fence from the list.

dma_fence_is_signaled_locked() tries to release/free the fence and hold the lock in the process.

We fix that by changing the order operation and clean up the list and rb-tree first.

v2: Drop fence get/put dance and manipulate the list first (Chris Wilson)

Cc: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Gustavo Padovan gustavo.padovan@collabora.com Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Link: https://patchwork.freedesktop.org/patch/msgid/20170729152217.8362-2-gustavo@... [s/dma_fence/fence/g - gregkh] Cc: Jisheng Zhang Jisheng.Zhang@synaptics.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- drivers/dma-buf/sw_sync.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -213,11 +213,21 @@ static void sync_timeline_signal(struct obj->value += inc;

list_for_each_entry_safe(pt, next, &obj->pt_list, link) { - if (!fence_is_signaled_locked(&pt->base)) + if (!timeline_fence_signaled(&pt->base)) break;

list_del_init(&pt->link); rb_erase(&pt->node, &obj->pt_tree); + + /* + * A signal callback may release the last reference to this + * fence, causing it to be freed. That operation has to be + * last to avoid a use after free inside this loop, and must + * be after we remove the fence from the timeline in order to + * prevent deadlocking on timeline->lock inside + * timeline_fence_release(). + */ + fence_signal_locked(&pt->base); }

spin_unlock_irq(&obj->lock);

Patches currently in stable-queue which might be from gustavo.padovan@collabora.com are

queue-4.9/dma-buf-sw-sync-fix-the-is-signaled-test-to-handle-u32-wraparound.patch queue-4.9/dma-buf-sw-sync-fix-locking-around-sync_timeline-lists.patch queue-4.9/dma-buf-sw_sync-clean-up-list-before-signaling-the-fence.patch queue-4.9/dma-buf-sw-sync-reduce-irqsave-irqrestore-from-known-context.patch queue-4.9/dma-buf-sw_sync-move-timeline_fence_ops-around.patch queue-4.9/dma-buf-sw-sync-prevent-user-overflow-on-timeline-advance.patch queue-4.9/dma-buf-sw_sync-force-signal-all-unsignaled-fences-on-dying-timeline.patch queue-4.9/dma-buf-sw-sync-use-an-rbtree-to-sort-fences-in-the-timeline.patch queue-4.9/dma-buf-sw-sync-sync_pt-is-private-and-of-fixed-size.patch queue-4.9/dma-buf-dma-fence-extract-__dma_fence_is_later.patch