[PATCH v2 05/12] conf, fwd: Record "auto" port forwards in forwarding table

[David Gibson <david@gibson.dropbear.id.au>]

Currently the forwarding table records details of explicit port forwards,
but nothing for -[tTuU] auto.  That looks a little odd on the debug output,
and will be a problem for future changes.

Extend the forward table to have entries for auto-scanned forwards, using
a new FWD_SCAN flag.  For now the mechanism of auto port forwarding isn't
updated, and we can only create a single FWD_SCAN entry per protocol and
direction.  We'll better integrate auto scanning with other forward table
mechanics in future.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 conf.c | 34 ++++++++++++++++++++++++++++------
 fwd.c  | 12 +++++++-----
 fwd.h  |  2 ++
 3 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/conf.c b/conf.c
index af9e82f5..9d94e449 100644
--- a/conf.c
+++ b/conf.c
@@ -135,7 +135,7 @@ static int parse_port_range(const char *s, char **endptr,
  * @ifname:	Listening interface
  * @first:	First port to forward
  * @last:	Last port to forward
- * @exclude:	Bitmap of ports to exclude
+ * @exclude:	Bitmap of ports to exclude (may be NULL)
  * @to:		Port to translate @first to when forwarding
  * @flags:	Flags for forwarding entries
  */
@@ -158,11 +158,11 @@ static void conf_ports_range_except(const struct ctx *c, char optname,
 	}
 
 	for (base = first; base <= last; base++) {
-		if (bitmap_isset(exclude, base))
+		if (exclude && bitmap_isset(exclude, base))
 			continue;
 
 		for (i = base; i <= last; i++) {
-			if (bitmap_isset(exclude, i))
+			if (exclude && bitmap_isset(exclude, i))
 				break;
 
 			if (bitmap_isset(fwd->map, i)) {
@@ -170,12 +170,13 @@ static void conf_ports_range_except(const struct ctx *c, char optname,
 "Altering mapping of already mapped port number: %s", optarg);
 			}
 
-			bitmap_set(fwd->map, i);
+			if (!(flags & FWD_SCAN))
+				bitmap_set(fwd->map, i);
 			fwd->delta[i] = delta;
 
-			if (optname == 't')
+			if (!(flags & FWD_SCAN) && optname == 't')
 				ret = tcp_listen(c, PIF_HOST, addr, ifname, i);
-			else if (optname == 'u')
+			else if (!(flags & FWD_SCAN) && optname == 'u')
 				ret = udp_listen(c, PIF_HOST, addr, ifname, i);
 			else
 				/* No way to check in advance for -T and -U */
@@ -2189,6 +2190,27 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->udp.fwd_out.mode)
 		c->udp.fwd_out.mode = fwd_default;
 
+	if (c->tcp.fwd_in.mode == FWD_AUTO) {
+		conf_ports_range_except(c, 't', "auto", &c->tcp.fwd_in,
+					NULL, NULL, 1, NUM_PORTS - 1,
+					NULL, 1, FWD_SCAN);
+	}
+	if (c->tcp.fwd_out.mode == FWD_AUTO) {
+		conf_ports_range_except(c, 'T', "auto", &c->tcp.fwd_out,
+					NULL, "lo", 1, NUM_PORTS - 1,
+					NULL, 1, FWD_SCAN);
+	}
+	if (c->udp.fwd_in.mode == FWD_AUTO) {
+		conf_ports_range_except(c, 'u', "auto", &c->udp.fwd_in,
+					NULL, NULL, 1, NUM_PORTS - 1,
+					NULL, 1, FWD_SCAN);
+	}
+	if (c->udp.fwd_out.mode == FWD_AUTO) {
+		conf_ports_range_except(c, 'U', "auto", &c->udp.fwd_out,
+					NULL, "lo", 1, NUM_PORTS - 1,
+					NULL, 1, FWD_SCAN);
+	}
+
 	if (!c->quiet)
 		conf_print(c);
 }
diff --git a/fwd.c b/fwd.c
index a8477607..5e5dc58c 100644
--- a/fwd.c
+++ b/fwd.c
@@ -331,7 +331,7 @@ void fwd_table_add(struct fwd_ports *fwd, uint8_t flags,
 		   in_port_t first, in_port_t last, in_port_t to)
 {
 	/* Flags which can be set from the caller */
-	const uint8_t allowed_flags = FWD_WEAK;
+	const uint8_t allowed_flags = FWD_WEAK | FWD_SCAN;
 	struct fwd_entry *new;
 
 	ASSERT(!(flags & ~allowed_flags));
@@ -371,6 +371,7 @@ void fwd_table_print(const struct fwd_ports *fwd)
 	for (i = 0; i < fwd->count; i++) {
 		const struct fwd_entry *fe = &fwd->tab[i];
 		const char *weak = fe->flags & FWD_WEAK ? " WEAK" : "";
+		const char *scan = fe->flags & FWD_SCAN ? " AUTO" : "";
 		const char *percent = *fe->ifname ? "%" : "";
 		char addr[INANY_ADDRSTRLEN] = "*";
 
@@ -378,13 +379,14 @@ void fwd_table_print(const struct fwd_ports *fwd)
 			inany_ntop(&fe->addr, addr, sizeof(addr));
 
 		if (fe->first == fe->last) {
-			info("    [%s]%s%s:%hu  =>  %hu %s",
+			info("    [%s]%s%s:%hu  =>  %hu %s%s",
 			     addr, percent, fe->ifname,
-			     fe->first, fe->to, weak);
+			     fe->first, fe->to, weak, scan);
 		} else {
-			info("    [%s]%s%s:%hu-%hu  =>  %hu-%hu %s",
+			info("    [%s]%s%s:%hu-%hu  =>  %hu-%hu %s%s",
 			     addr, percent, fe->ifname, fe->first, fe->last,
-			     fe->to, fe->last - fe->first + fe->to, weak);
+			     fe->to, fe->last - fe->first + fe->to,
+			     weak, scan);
 		}
 	}
 }
diff --git a/fwd.h b/fwd.h
index 21f00cf8..eef507c6 100644
--- a/fwd.h
+++ b/fwd.h
@@ -26,6 +26,7 @@ bool fwd_port_is_ephemeral(in_port_t port);
  * @flags:	Flag mask
  * 	FWD_DUAL_STACK - forward both IPv4 and IPv6 (requires @addr be ::)
  *	FWD_WEAK - Don't give an error if binds fail for some forwards
+ *	FWD_SCAN - Only forward if we scan a listener on the target
  *
  * FIXME: @addr and @ifname currently ignored for outbound tables
  */
@@ -35,6 +36,7 @@ struct fwd_entry {
 	in_port_t first, last, to;
 #define FWD_DUAL_STACK		BIT(0)
 #define FWD_WEAK		BIT(1)
+#define FWD_SCAN		BIT(2)
 	uint8_t flags;
 };
 
-- 
2.52.0