svcrpc: fix handling of too-short rpc's

If we detect that an rpc is too short, we abort and close the
connection.  Except, there's a bug here: we're leaving sk_datalen
nonzero without leaving any pages in the sk_pages array.  The most
likely result of the inconsistency is a subsequent crash in
svc_tcp_clear_pages.

Also demote the BUG_ON in svc_tcp_clear_pages to a WARN.

Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/svcsock.c

@@ -917,7 +917,10 @@ static void svc_tcp_clear_pages(struct svc_sock *svsk)
 	len = svsk->sk_datalen;
 	npages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	for (i = 0; i < npages; i++) {
-		BUG_ON(svsk->sk_pages[i] == NULL);
+		if (svsk->sk_pages[i] == NULL) {
+			WARN_ON_ONCE(1);
+			continue;
+		}
 		put_page(svsk->sk_pages[i]);
 		svsk->sk_pages[i] = NULL;
 	}
@@ -1092,8 +1095,10 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 		goto err_noclose;
 	}
 
-	if (svc_sock_reclen(svsk) < 8)
+	if (svc_sock_reclen(svsk) < 8) {
+		svsk->sk_datalen = 0;
 		goto err_delete; /* client is nuts. */
+	}
 
 	rqstp->rq_arg.len = svsk->sk_datalen;
 	rqstp->rq_arg.page_base = 0;