[PATCH] tcp, udp: Don't initialise IPv6/IPv4 sockets if IPv4/IPv6 are not enabled

[Stefano Brivio <sbrivio@redhat.com>]

If we disable a given IP version automatically (no corresponding
default route on host) or administratively (--ipv4-only or
--ipv6-only options), we don't initialise related buffers and
services (DHCP for IPv4, NDP and DHCPv6 for IPv6). The "tap"
handlers will also ignore packets with a disabled IP version.

However, in commit 3c6ae625101a ("conf, tcp, udp: Allow address
specification for forwarded ports") I happily changed socket
initialisation functions to take AF_UNSPEC meaning "any enabled
IP version", but I forgot to add checks back for the "enabled"
part.

Reported by Paul: on a host without default IPv6 route, but IPv6
enabled, connect, using IPv6, to a port handled by pasta, which
tries to send data to a tap device without initialised buffers
for that IP version and exits because the resulting write() fails.

Simpler way to reproduce: pasta -6 and inbound IPv4 connection, or
pasta -4 and inbound IPv6 connection.

Reported-by: Paul Holzinger <pholzing@redhat.com>
Fixes: 3c6ae625101a ("conf, tcp, udp: Allow address specification for forwarded ports")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tcp.c | 4 ++--
 udp.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tcp.c b/tcp.c
index 713248f..d043123 100644
--- a/tcp.c
+++ b/tcp.c
@@ -3213,9 +3213,9 @@ static void tcp_sock_init6(const struct ctx *c, int ns,
 void tcp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		   const void *addr, const char *ifname, in_port_t port)
 {
-	if (af == AF_INET || af == AF_UNSPEC)
+	if ((af == AF_INET  || af == AF_UNSPEC) && c->ifi4)
 		tcp_sock_init4(c, ns, addr, ifname, port);
-	if (af == AF_INET6 || af == AF_UNSPEC)
+	if ((af == AF_INET6 || af == AF_UNSPEC) && c->ifi6)
 		tcp_sock_init6(c, ns, addr, ifname, port);
 }
 
diff --git a/udp.c b/udp.c
index 42a17a7..ff7f993 100644
--- a/udp.c
+++ b/udp.c
@@ -1129,7 +1129,7 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 					    c->udp.fwd_in.f.delta[port]);
 	}
 
-	if (af == AF_INET || af == AF_UNSPEC) {
+	if ((af == AF_INET || af == AF_UNSPEC) && c->ifi4) {
 		if (!addr && c->mode == MODE_PASTA)
 			bind_addr = &c->ip4.addr;
 		else
@@ -1162,7 +1162,7 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		}
 	}
 
-	if (af == AF_INET6 || af == AF_UNSPEC) {
+	if ((af == AF_INET6 || af == AF_UNSPEC) && c->ifi6) {
 		if (!addr && c->mode == MODE_PASTA)
 			bind_addr = &c->ip6.addr;
 		else
-- 
@@ -1129,7 +1129,7 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 					    c->udp.fwd_in.f.delta[port]);
 	}
 
-	if (af == AF_INET || af == AF_UNSPEC) {
+	if ((af == AF_INET || af == AF_UNSPEC) && c->ifi4) {
 		if (!addr && c->mode == MODE_PASTA)
 			bind_addr = &c->ip4.addr;
 		else
@@ -1162,7 +1162,7 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		}
 	}
 
-	if (af == AF_INET6 || af == AF_UNSPEC) {
+	if ((af == AF_INET6 || af == AF_UNSPEC) && c->ifi6) {
 		if (!addr && c->mode == MODE_PASTA)
 			bind_addr = &c->ip6.addr;
 		else
-- 
2.35.1