[PATCH 1/2] dma-buf/dma-fence: fix checking signaling bit for timeline and driver name

[Christian König]

The patch "dma-buf: dma-fence: Fix potential NULL pointer dereference"
changed the check to test for the ops pointer instead of the signaled
bit to avoid a potential NULL dereference when the ops pointer has been
cleared.

The problem is now that the ops pointer is cleared only when neither the
release nor the wait callback is implemented and this isn't true for a lot
of dma_fence implementations yet. So those implementations lost the RCU
protection after signaling of the returned string resulting in potential
use after free.

Add the signaling check additional to the ops pointer check so that we
have both the protection against NULL dereference as well as the RCU
protection after signaling for the returned string.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Fixes: 035219a760ed ("dma-buf: dma-fence: Fix potential NULL pointer dereference")
CC: stable@xxxxxxxxxxxxxxx # 7.2+
Reported-by: Jonghyuk Kim(MalHyuk) <malhyuk97@xxxxxxxxx>
Tested-by: Jonghyuk Kim(MalHyuk) <malhyuk97@xxxxxxxxx>
---
 drivers/dma-buf/dma-fence.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 05090fb0fd5a..e92f9df8d63c 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -1170,7 +1170,7 @@ const char __rcu *dma_fence_driver_name(struct dma_fence *fence)
 
 	/* RCU protection is required for safe access to returned string */
 	ops = rcu_dereference(fence->ops);
-	if (ops)
+	if (!dma_fence_test_signaled_flag(fence) && ops)
 		return (const char __rcu *)ops->get_driver_name(fence);
 	else
 		return (const char __rcu *)"detached-driver";
@@ -1203,7 +1203,7 @@ const char __rcu *dma_fence_timeline_name(struct dma_fence *fence)
 
 	/* RCU protection is required for safe access to returned string */
 	ops = rcu_dereference(fence->ops);
-	if (ops)
+	if (!dma_fence_test_signaled_flag(fence) && ops)
 		return (const char __rcu *)ops->get_timeline_name(fence);
 	else
 		return (const char __rcu *)"signaled-timeline";
-- 
2.43.0