CVE-2024-57927

In the Linux kernel, the following vulnerability has been resolved:

nfs: Fix oops in nfsnetfsinit_request() when copying to cache

When netfslib wants to copy some data that has just been read on behalf of nfs, it creates a new write request and calls nfsnetfsinitrequest() to initialise it, but with a NULL file pointer. This causes nfsfileopencontext() to oops - however, we don't actually need the nfs context as we're only going to write to the cache.

Fix this by just returning if we aren't given a file pointer and emit a warning if the request was for something other than copy-to-cache.

Further, fix nfsnetfsfree_request() so that it doesn't try to free the context if the pointer is NULL.