From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx> commit a3f7c10a269d5b77dd5822ade822643ced3057f0 upstream. 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. Signed-off-by: Christian König <christian.koenig@xxxxxxx> Reviewed-by: Jason Ekstrand <jason.ekstrand@xxxxxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20220810172617.140047-1-christian.koenig@xxxxxxx Cc: stable@xxxxxxxxxxxxxxx # v5.19+ Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/dma-buf/dma-resv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- 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 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);
