Fix widespread off-by-one error dealing with port numbers

Port numbers (for both TCP and UDP) are 16-bit, and so fit exactly into a
'short'.  USHRT_MAX is therefore the maximum port number and this is widely
used in the code.  Unfortunately, a lot of those places don't actually
want the maximum port number (USHRT_MAX == 65535), they want the total
number of ports (65536).  This leads to a number of potentially nasty
consequences:

 * We have buffer overruns on the port_fwd::delta array if we try to use
   port 65535
 * We have similar potential overruns for the tcp_sock_* arrays
 * Interestingly udp_act had the correct size, but we can calculate it in
   a more direct manner
 * We have a logical overrun of the ports bitmap as well, although it will
   just use an unused bit in the last byte so isnt harmful
 * Many loops don't consider port 65535 (which does mitigate some but not
   all of the buffer overruns above)
 * In udp_invert_portmap() we incorrectly compute the reverse port
   translation for return packets

Correct all these by using a new NUM_PORTS defined explicitly for this
purpose.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

conf.c

@@ -209,7 +209,7 @@ static int conf_ports(const struct ctx *c, char optname, const char *optarg,
 		if (sep == p)
 			break;
 
-		if (port > USHRT_MAX || errno)
+		if (port >= NUM_PORTS || errno)
 			goto bad;
 
 		switch (*sep) {
@@ -276,7 +276,7 @@ static int conf_ports(const struct ctx *c, char optname, const char *optarg,
 		if (sep == p)
 			break;
 
-		if (port > USHRT_MAX || errno)
+		if (port >= NUM_PORTS || errno)
 			goto bad;
 
 		/* -p 22

port_fwd.h

@@ -7,6 +7,9 @@
 #ifndef PORT_FWD_H
 #define PORT_FWD_H
 
+/* Number of ports for both TCP and UDP */
+#define	NUM_PORTS	(1U << 16)
+
 enum port_fwd_mode {
 	FWD_SPEC = 1,
 	FWD_NONE,
@@ -14,7 +17,7 @@ enum port_fwd_mode {
 	FWD_ALL,
 };
 
-#define PORT_BITMAP_SIZE	DIV_ROUND_UP(USHRT_MAX, 8)
+#define PORT_BITMAP_SIZE	DIV_ROUND_UP(NUM_PORTS, 8)
 
 /**
  * port_fwd - Describes port forwarding for one protocol and direction
@@ -25,7 +28,7 @@ enum port_fwd_mode {
 struct port_fwd {
 	enum port_fwd_mode mode;
 	uint8_t map[PORT_BITMAP_SIZE];
-	in_port_t delta[USHRT_MAX];
+	in_port_t delta[NUM_PORTS];
 };
 
 #endif /* PORT_FWD_H */

tcp.c

@@ -547,9 +547,9 @@ static const char *tcp_flag_str[] __attribute((__unused__)) = {
 };
 
 /* Listening sockets, used for automatic port forwarding in pasta mode only */
-static int tcp_sock_init_lo	[USHRT_MAX][IP_VERSIONS];
-static int tcp_sock_init_ext	[USHRT_MAX][IP_VERSIONS];
-static int tcp_sock_ns		[USHRT_MAX][IP_VERSIONS];
+static int tcp_sock_init_lo	[NUM_PORTS][IP_VERSIONS];
+static int tcp_sock_init_ext	[NUM_PORTS][IP_VERSIONS];
+static int tcp_sock_ns		[NUM_PORTS][IP_VERSIONS];
 
 /* Table of destinations with very low RTT (assumed to be local), LRU */
 static struct in6_addr low_rtt_dst[LOW_RTT_TABLE_SIZE];
@@ -3186,7 +3186,7 @@ static int tcp_sock_init_ns(void *arg)
 
 	ns_enter(c);
 
-	for (port = 0; port < USHRT_MAX; port++) {
+	for (port = 0; port < NUM_PORTS; port++) {
 		if (!bitmap_isset(c->tcp.fwd_out.map, port))
 			continue;
 
@@ -3386,7 +3386,7 @@ static int tcp_port_rebind(void *arg)
 	if (a->bind_in_ns) {
 		ns_enter(a->c);
 
-		for (port = 0; port < USHRT_MAX; port++) {
+		for (port = 0; port < NUM_PORTS; port++) {
 			if (!bitmap_isset(a->c->tcp.fwd_out.map, port)) {
 				if (tcp_sock_ns[port][V4] >= 0) {
 					close(tcp_sock_ns[port][V4]);
@@ -3410,7 +3410,7 @@ static int tcp_port_rebind(void *arg)
 				tcp_sock_init(a->c, 1, AF_UNSPEC, NULL, port);
 		}
 	} else {
-		for (port = 0; port < USHRT_MAX; port++) {
+		for (port = 0; port < NUM_PORTS; port++) {
 			if (!bitmap_isset(a->c->tcp.fwd_in.map, port)) {
 				if (tcp_sock_init_ext[port][V4] >= 0) {
 					close(tcp_sock_init_ext[port][V4]);

udp.c

@@ -164,8 +164,8 @@ struct udp_splice_port {
 };
 
 /* Port tracking, arrays indexed by packet source port (host order) */
-static struct udp_tap_port	udp_tap_map	[IP_VERSIONS][USHRT_MAX];
-static struct udp_splice_port	udp_splice_map	[IP_VERSIONS][USHRT_MAX];
+static struct udp_tap_port	udp_tap_map	[IP_VERSIONS][NUM_PORTS];
+static struct udp_splice_port	udp_splice_map	[IP_VERSIONS][NUM_PORTS];
 
 enum udp_act_type {
 	UDP_ACT_TAP,
@@ -175,7 +175,7 @@ enum udp_act_type {
 };
 
 /* Activity-based aging for bindings */
-static uint8_t udp_act[IP_VERSIONS][UDP_ACT_TYPE_MAX][(USHRT_MAX + 1) / 8];
+static uint8_t udp_act[IP_VERSIONS][UDP_ACT_TYPE_MAX][DIV_ROUND_UP(NUM_PORTS, 8)];
 
 /* Static buffers */
 
@@ -271,7 +271,7 @@ static void udp_invert_portmap(struct udp_port_fwd *fwd)
 		in_port_t delta = fwd->f.delta[i];
 
 		if (delta)
-			fwd->rdelta[(in_port_t)i + delta] = USHRT_MAX - delta;
+			fwd->rdelta[(in_port_t)i + delta] = NUM_PORTS - delta;
 	}
 }
 
@@ -1198,7 +1198,7 @@ int udp_sock_init_ns(void *arg)
 	if (ns_enter(c))
 		return 0;
 
-	for (dst = 0; dst < USHRT_MAX; dst++) {
+	for (dst = 0; dst < NUM_PORTS; dst++) {
 		if (!bitmap_isset(c->udp.fwd_out.f.map, dst))
 			continue;
 

udp.h

@@ -50,7 +50,7 @@ union udp_epoll_ref {
  */
 struct udp_port_fwd {
 	struct port_fwd f;
-	in_port_t rdelta[USHRT_MAX];
+	in_port_t rdelta[NUM_PORTS];
 };
 
 /**