svcrpc: fix UDP on servers with lots of threads

J. Bruce Fields · J. Bruce Fields · commit b7e5034cbecf · 2019-02-21T10:17:36.000-05:00
James Pearson found that an NFS server stopped responding to UDP
requests if started with more than 1017 threads.

sv_max_mesg is about 2^20, so that is probably where the calculation
performed by

	svc_sock_setbufsize(svsk-&gt;sk_sock,
                            (serv-&gt;sv_nrthreads+3) * serv-&gt;sv_max_mesg,
                            (serv-&gt;sv_nrthreads+3) * serv-&gt;sv_max_mesg);

starts to overflow an int.

Reported-by: James Pearson &lt;jcpearson@gmail.com&gt;
Tested-by: James Pearson &lt;jcpearson@gmail.com&gt;
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields &lt;bfields@redhat.com&gt;
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
@@ -349,12 +349,16 @@ static ssize_t svc_recvfrom(struct svc_rqst *rqstp, struct kvec *iov,
 /*
  * Set socket snd and rcv buffer lengths
  */
-static void svc_sock_setbufsize(struct socket *sock, unsigned int snd,
-				unsigned int rcv)
+static void svc_sock_setbufsize(struct svc_sock *svsk, unsigned int nreqs)
 {
+	unsigned int max_mesg = svsk->sk_xprt.xpt_server->sv_max_mesg;
+	struct socket *sock = svsk->sk_sock;
+
+	nreqs = min(nreqs, INT_MAX / 2 / max_mesg);
+
 	lock_sock(sock->sk);
-	sock->sk->sk_sndbuf = snd * 2;
-	sock->sk->sk_rcvbuf = rcv * 2;
+	sock->sk->sk_sndbuf = nreqs * max_mesg * 2;
+	sock->sk->sk_rcvbuf = nreqs * max_mesg * 2;
 	sock->sk->sk_write_space(sock->sk);
 	release_sock(sock->sk);
 }
@@ -516,9 +520,7 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
 	     * provides an upper bound on the number of threads
 	     * which will access the socket.
 	     */
-	    svc_sock_setbufsize(svsk->sk_sock,
-				(serv->sv_nrthreads+3) * serv->sv_max_mesg,
-				(serv->sv_nrthreads+3) * serv->sv_max_mesg);
+	    svc_sock_setbufsize(svsk, serv->sv_nrthreads + 3);
 
 	clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
 	skb = NULL;
@@ -681,9 +683,7 @@ static void svc_udp_init(struct svc_sock *svsk, struct svc_serv *serv)
 	 * receive and respond to one request.
 	 * svc_udp_recvfrom will re-adjust if necessary
 	 */
-	svc_sock_setbufsize(svsk->sk_sock,
-			    3 * svsk->sk_xprt.xpt_server->sv_max_mesg,
-			    3 * svsk->sk_xprt.xpt_server->sv_max_mesg);
+	svc_sock_setbufsize(svsk, 3);
 
 	/* data might have come in before data_ready set up */
 	set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
