NFSD: fix use-after-free in nfsd4_ssc_setup_dul()

jira VULN-8056
cve CVE-2023-1652
commit-author Xingyuan Mo <hdthky0@gmail.com>
commit e6cf91b

If signal_pending() returns true, schedule_timeout() will not be executed,
causing the waiting task to remain in the wait queue.
Fixed by adding a call to finish_wait(), which ensures that the waiting
task will always be removed from the wait queue.

Fixes: f4e44b3 ("NFSD: delay unmount source's export after inter-server copy completed.")
	Signed-off-by: Xingyuan Mo <hdthky0@gmail.com>
	Reviewed-by: Jeff Layton <jlayton@kernel.org>
	Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
(cherry picked from commit e6cf91b)
	Signed-off-by: Anmol Jain <ajain@ciq.com>

Author: jainanmol84

fs/nfsd/nfs4proc.c

@@ -1328,6 +1328,7 @@ static __be32 nfsd4_ssc_setup_dul(struct nfsd_net *nn, char *ipaddr,
 			/* allow 20secs for mount/unmount for now - revisit */
 			if (signal_pending(current) ||
 					(schedule_timeout(20*HZ) == 0)) {
+				finish_wait(&nn->nfsd_ssc_waitq, &wait);
 				kfree(work);
 				return nfserr_eagain;
 			}