Limit outgoing packet queue length

If we were using TCP and the socket stalled, we'd just keep sucking
packets from the kernel, allocating memory and queuing them
internally with no limit except the size of the swap space. Not clever.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

cstp.c

@@ -549,6 +549,7 @@ int cstp_mainloop(struct openconnect_info *vpninfo, int *timeout)
 	while (vpninfo->dtls_fd == -1 && vpninfo->outgoing_queue) {
 		struct pkt *this = vpninfo->outgoing_queue;
 		vpninfo->outgoing_queue = this->next;
+		vpninfo->outgoing_qlen--;
 
 		if (vpninfo->deflate) {
 			unsigned char *adler;

dtls.c

@@ -445,6 +445,7 @@ int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 		int ret;
 
 		vpninfo->outgoing_queue = this->next;
+		vpninfo->outgoing_qlen--;
 
 		/* One byte of header */
 		this->hdr[7] = AC_PKT_DATA;
@@ -461,6 +462,7 @@ int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 				ERR_print_errors_fp(stderr);
 				dtls_restart(vpninfo);
 				vpninfo->outgoing_queue = this;
+				vpninfo->outgoing_qlen++;
 			}
 			return 1;
 		}

mainloop.c

@@ -93,7 +93,9 @@ int vpn_mainloop(struct openconnect_info *vpninfo)
 		did_work += cstp_mainloop(vpninfo, &timeout);
 		if (vpninfo->quit_reason)
 			break;
-
+
+		/* Tun must be last because it will set/clear its bit
+		   in the select_rfds according to the queue length */
 		did_work += tun_mainloop(vpninfo, &timeout);
 		if (vpninfo->quit_reason)
 			break;

openconnect.h

@@ -53,6 +53,9 @@ struct vpn_option {
 #define KA_KEEPALIVE	3
 #define KA_REKEY	4
 
+
+#define MAX_Q_LEN 10
+
 struct keepalive_info {
 	int dpd;
 	int keepalive;
@@ -135,6 +138,7 @@ struct openconnect_info {
 
 	struct pkt *incoming_queue;
 	struct pkt *outgoing_queue;
+	int outgoing_qlen;
 
 	socklen_t peer_addrlen;
 	struct sockaddr *peer_addr;

tun.c

@@ -304,9 +304,20 @@ int tun_mainloop(struct openconnect_info *vpninfo, int *timeout)
 	int len;
 	int work_done = 0;
 
-	while ( (len = read(vpninfo->tun_fd, buf, sizeof(buf))) > 0) {
-		queue_new_packet(&vpninfo->outgoing_queue, AF_INET, buf, len);
-		work_done = 1;
+	if (FD_ISSET(vpninfo->tun_fd, &vpninfo->select_rfds)) {
+		while ((len = read(vpninfo->tun_fd, buf, sizeof(buf))) > 0) {
+			if (queue_new_packet(&vpninfo->outgoing_queue, AF_INET, buf, len))
+				break;
+
+			work_done = 1;
+			vpninfo->outgoing_qlen++;
+			if (vpninfo->outgoing_qlen == MAX_Q_LEN) {
+				FD_CLR(vpninfo->tun_fd, &vpninfo->select_rfds);
+				break;
+			}
+		}
+	} else if (vpninfo->outgoing_qlen < MAX_Q_LEN) {
+		FD_SET(vpninfo->tun_fd, &vpninfo->select_rfds);
 	}
 
 	/* The kernel returns -ENOMEM when the queue is full, so theoretically