On Wed, Aug 10, 2022 at 12:26 PM Christian König < ckoenig.leichtzumerken@gmail.com> wrote:

Previously when we added a fence to a dma_resv object we always assumed the the newer than all the existing fences.

With Jason's work to add an UAPI to explicit export/import that's not necessary the case any more. So without this check we would allow userspace to force the kernel into an use after free error.

Since the change is very small and defensive it's probably a good idea to backport this to stable kernels as well just in case others are using the dma_resv object in the same way.

Especially in the new world of dma_resv being a "bag of fences", I think this makes a lot of sense.

Reviewed-by: Jason Ekstrand jason.ekstrand@collabora.com

Signed-off-by: Christian König christian.koenig@amd.com

drivers/dma-buf/dma-resv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 205acb2c744d..e3885c90a3ac 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -295,7 +295,8 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence, enum dma_resv_usage old_usage;

            dma_resv_list_entry(fobj, i, obj, &old, &old_usage);

•           if ((old->context == fence->context && old_usage >= usage)
  

||

•           if ((old->context == fence->context && old_usage >= usage
  

&&

•                dma_fence_is_later(fence, old)) ||
                dma_fence_is_signaled(old)) {
                    dma_resv_list_set(fobj, i, fence, usage);
                    dma_fence_put(old);
  

-- 2.25.1