conf: Don't fail if the template interface doesn't have a MAC address

...simply resort to using locally-administered address (LAA) as
host-side source, instead.

Pick 02:00:00:00:00:00, to make it clear that we don't actually care
about that address, and also to match the 00 (Administratively
Assigned Identifier) quadrant of SLAP (RFC 8948).

Otherwise, pasta refuses to start if the template is a tun or
Wireguard interface.

Link: https://bugs.passt.top/show_bug.cgi?id=49
Link: https://github.com/containers/podman/issues/22320
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 9 insertions, 4 deletions

diff --git a/conf.c b/conf.c
index 90d3436..3f30725 100644
--- a/conf.c
+++ b/conf.c
@@ -629,10 +629,12 @@ static unsigned int conf_ip4(unsigned int ifi,
 			    if_indextoname(ifi, ifname), strerror(-rc));
 			return 0;
 		}
+
+		if (MAC_IS_ZERO(mac))
+			memcpy(mac, MAC_LAA, ETH_ALEN);
 	}
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr) ||
-	    MAC_IS_ZERO(mac))
+	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
 		return 0;
 
 	return ifi;
@@ -688,11 +690,13 @@ static unsigned int conf_ip6(unsigned int ifi,
 			    if_indextoname(ifi, ifname), strerror(-rc));
 			return 0;
 		}
+
+		if (MAC_IS_ZERO(mac))
+			memcpy(mac, MAC_LAA, ETH_ALEN);
 	}
 
 	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
-	    IN6_IS_ADDR_UNSPECIFIED(&ip6->addr_ll) ||
-	    MAC_IS_ZERO(mac))
+	    IN6_IS_ADDR_UNSPECIFIED(&ip6->addr_ll))
 		return 0;
 
 	return ifi;
diff --git a/util.h b/util.h
index 8c37729..ef01001 100644
--- a/util.h
+++ b/util.h
@@ -91,6 +91,7 @@
 #define PORT_IS_EPHEMERAL(port) ((port) >= PORT_EPHEMERAL_MIN)
 
 #define MAC_ZERO		((uint8_t [ETH_ALEN]){ 0 })
+#define MAC_LAA			((uint8_t [ETH_ALEN]){ BIT(1), 0, 0, 0, 0, 0 })
 #define MAC_IS_ZERO(addr)	(!memcmp((addr), MAC_ZERO, ETH_ALEN))
 
 #ifndef __bswap_constant_16