nfsd: fix corrupted reply to badly ordered compound

BugLink: https://bugs.launchpad.net/bugs/1798770

[ Upstream commit 5b7b15ae ]

We're encoding a single op in the reply but leaving the number of ops
zero, so the reply makes no sense.

Somewhat academic as this isn't a case any real client will hit, though
in theory perhaps that could change in a future protocol extension.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/nfsd/nfs4proc.c

@@ -1632,6 +1632,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp,
 	if (status) {
 		op = &args->ops[0];
 		op->status = status;
+		resp->opcnt = 1;
 		goto encode_op;
 	}