[XFRM]: IPsec tunnel wildcard address support

When the source address of a tunnel is given as 0.0.0.0 do a routing lookup
to get the real source address for the destination and fill that into the
acquire message. This allows to specify policies like this:

spdadd 172.16.128.13/32 172.16.0.0/20 any -P out ipsec
esp/tunnel/0.0.0.0-x.x.x.x/require;
spdadd 172.16.0.0/20 172.16.128.13/32 any -P in ipsec
esp/tunnel/x.x.x.x-0.0.0.0/require;

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/xfrm4_state.c

···
 	x->props.saddr = tmpl->saddr;
 	if (x->props.saddr.a4 == 0)
 		x->props.saddr.a4 = saddr->a4;
+	if (tmpl->mode && x->props.saddr.a4 == 0) {
+		struct rtable *rt;
+	        struct flowi fl_tunnel = {
+        	        .nl_u = {
+        			.ip4_u = {
+					.daddr = x->id.daddr.a4,
+				}
+			}
+		};
+		if (!xfrm_dst_lookup((struct xfrm_dst **)&rt,
+		                     &fl_tunnel, AF_INET)) {
+			x->props.saddr.a4 = rt->rt_src;
+			dst_release(&rt->u.dst);
+		}
+	}
 	x->props.mode = tmpl->mode;
 	x->props.reqid = tmpl->reqid;
 	x->props.family = AF_INET;

net/ipv6/xfrm6_state.c

···
 #include <linux/pfkeyv2.h>
 #include <linux/ipsec.h>
 #include <net/ipv6.h>
+#include <net/addrconf.h>
 
 static struct xfrm_state_afinfo xfrm6_state_afinfo;
 
···
 	memcpy(&x->props.saddr, &tmpl->saddr, sizeof(x->props.saddr));
 	if (ipv6_addr_any((struct in6_addr*)&x->props.saddr))
 		memcpy(&x->props.saddr, saddr, sizeof(x->props.saddr));
+	if (tmpl->mode && ipv6_addr_any((struct in6_addr*)&x->props.saddr)) {
+		struct rt6_info *rt;
+		struct flowi fl_tunnel = {
+			.nl_u = {
+				.ip6_u = {
+					.daddr = *(struct in6_addr *)daddr,
+				}
+			}
+		};
+		if (!xfrm_dst_lookup((struct xfrm_dst **)&rt,
+		                     &fl_tunnel, AF_INET6)) {
+			ipv6_get_saddr(&rt->u.dst, (struct in6_addr *)daddr,
+			               (struct in6_addr *)&x->props.saddr);
+			dst_release(&rt->u.dst);
+		}
+	}
 	x->props.mode = tmpl->mode;
 	x->props.reqid = tmpl->reqid;
 	x->props.family = AF_INET6;