CVE-2024-53217 NFSD: Prevent NULL dereference in nfsd4_process_cb_update()

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent NULL dereference in nfsd4processcbupdate @ses is initialized to NULL. If nfsd4findbackchannel finds no available backchannel session, setupcallbackclient will try to dereference @ses and segfault...