dma-buf/dma-resv: check if the new fence is really later

In the Linux kernel, the following vulnerability has been resolved: dma-buf/dma-resv: check if the new fence is really later 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.