nfsd: zero out pointers after putting nfsd_files on COPY setup error

[ Upstream commit 1f0001d43d ]

At first, I thought this might be a source of nfsd_file overputs, but
the current callers seem to avoid an extra put when nfsd4_verify_copy
returns an error.

Still, it's "bad form" to leave the pointers filled out when we don't
have a reference to them anymore, and that might lead to bugs later.
Zero them out as a defensive coding measure.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/nfsd/nfs4proc.c

@@ -1088,8 +1088,10 @@ out:
 	return status;
 out_put_dst:
 	nfsd_file_put(*dst);
+	*dst = NULL;
 out_put_src:
 	nfsd_file_put(*src);
+	*src = NULL;
 	goto out;
 }