nfsd4: nfsd4_check_resp_size should check against whole buffer

Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -3762,7 +3762,6 @@ __be32 nfsd4_check_resp_size(struct nfsd4_compoundres *resp, u32 respsize)
 {
 	struct xdr_buf *buf = &resp->rqstp->rq_res;
 	struct nfsd4_session *session = resp->cstate.session;
-	int slack_bytes = (char *)resp->xdr.end - (char *)resp->xdr.p;
 
 	if (nfsd4_has_session(&resp->cstate)) {
 		struct nfsd4_slot *slot = resp->cstate.slot;
@@ -3775,7 +3774,7 @@ __be32 nfsd4_check_resp_size(struct nfsd4_compoundres *resp, u32 respsize)
 			return nfserr_rep_too_big_to_cache;
 	}
 
-	if (respsize > slack_bytes) {
+	if (buf->len + respsize > buf->buflen) {
 		WARN_ON_ONCE(nfsd4_has_session(&resp->cstate));
 		return nfserr_resource;
 	}