[PATCH net-next 04/13] amt: send the Membership Query over IPv6

[Omar Ramadan <omar@blockcast.net>]

After the Request, a relay answers each gateway with a Membership Query
through amt_send_membership_query(), which routes and transmits only
over IPv4.

Rather than adding an IPv6 twin of the function, move its routing and
transmit step into amt_udp_xmit(). Given an skb that already carries
the AMT message, a union amt_addr destination and the port pair, it
sends over the device's family: ip_route_output_key() and
udp_tunnel_xmit_skb() for IPv4, as before, and amt_route6() and
udp_tunnel6_xmit_skb(), which fills in the mandatory IPv6 UDP checksum,
for IPv6. Both use AMT_TOS, as the IPv4 path and the IPv6 control
messages do. udp_tunnel_xmit_skb() scrubs the skb in iptunnel_xmit(),
but udp_tunnel6_xmit_skb() does not, so the IPv6 path calls
skb_scrub_packet() itself. Otherwise the conntrack entry and extensions
of the inner packet would stay on the outer one, which conntrack would
then pass as an already tracked flow.

amt_send_membership_query() sizes its headroom for the outer family
with amt_ip_hlen(), builds the AMT header and hands the skb to
amt_udp_xmit(). The route lookup now runs after the header push; on a
route failure the caller still frees the skb. The relay's General
Query, which amt_send_igmp_gq() and amt_send_mld_gq() now send directly
through amt_send_membership_query(), takes the IPv6 path with no change
to those functions.

Assisted-by: LLM
Signed-off-by: Omar Ramadan <omar@blockcast.net>
---
 drivers/net/amt.c | 94 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 68 insertions(+), 26 deletions(-)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index eaa5637..5e8a74c 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -88,6 +88,11 @@ static bool amt_v6(const struct amt_dev *amt)
 	return IS_ENABLED(CONFIG_IPV6) && !ipv6_addr_any(&amt->local_ipv6);
 }
 
+static unsigned int amt_ip_hlen(const struct amt_dev *amt)
+{
+	return amt_v6(amt) ? sizeof(struct ipv6hdr) : sizeof(struct iphdr);
+}
+
 /* Copy the outer source address of a received message by value, so that
  * the caller may pull the skb afterwards.
  */
@@ -1098,6 +1103,65 @@ static void amt_req_work(struct work_struct *work)
 				 msecs_to_jiffies(100));
 }
 
+/* Route an AMT-encapsulated skb to @daddr and send it over the device's
+ * outer family. The caller has already pushed the AMT header.
+ */
+static int amt_udp_xmit(struct amt_dev *amt, struct sock *sk,
+			struct sk_buff *skb, const union amt_addr *daddr,
+			__be16 sport, __be16 dport)
+{
+	struct rtable *rt;
+	struct flowi4 fl4;
+
+	if (amt_v6(amt)) {
+		struct dst_entry *dst;
+
+		dst = amt_route6(amt, sk, &amt->local_ipv6, &daddr->ip6,
+				 sport, dport);
+		if (IS_ERR(dst)) {
+			netdev_dbg(amt->dev, "no route to %pI6c\n",
+				   &daddr->ip6);
+			return PTR_ERR(dst);
+		}
+		/* iptunnel_xmit() scrubs the IPv4 tunnel skb, but
+		 * udp_tunnel6_xmit_skb() does not, so drop the inner
+		 * packet's conntrack and extensions here. Links cannot
+		 * cross netns, so this is never xnet.
+		 */
+		skb_scrub_packet(skb, false);
+		udp_tunnel6_xmit_skb(dst, sk, skb, amt->dev, &amt->local_ipv6,
+				     &daddr->ip6, AMT_TOS,
+				     ip6_dst_hoplimit(dst), 0, sport, dport,
+				     false, 0);
+		return 0;
+	}
+
+	memset(&fl4, 0, sizeof(struct flowi4));
+	fl4.flowi4_oif         = amt->stream_dev->ifindex;
+	fl4.daddr              = daddr->ip4;
+	fl4.saddr              = amt->local_ip;
+	fl4.flowi4_dscp        = inet_dsfield_to_dscp(AMT_TOS);
+	fl4.flowi4_proto       = IPPROTO_UDP;
+	rt = ip_route_output_key(amt->net, &fl4);
+	if (IS_ERR(rt)) {
+		netdev_dbg(amt->dev, "no route to %pI4\n", &daddr->ip4);
+		return PTR_ERR(rt);
+	}
+
+	udp_tunnel_xmit_skb(rt, sk, skb,
+			    fl4.saddr,
+			    fl4.daddr,
+			    AMT_TOS,
+			    ip4_dst_hoplimit(&rt->dst),
+			    0,
+			    sport,
+			    dport,
+			    false,
+			    false,
+			    0);
+	return 0;
+}
+
 static bool amt_send_membership_update(struct amt_dev *amt,
 				       struct sk_buff *skb,
 				       bool v6)
@@ -1230,8 +1294,6 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 				      bool v6)
 {
 	struct amt_header_membership_query *amtmq;
-	struct rtable *rt;
-	struct flowi4 fl4;
 	struct sock *sk;
 	int err;
 
@@ -1240,23 +1302,11 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 		return true;
 
 	err = skb_cow_head(skb, LL_RESERVED_SPACE(amt->dev) + sizeof(*amtmq) +
-			   sizeof(struct iphdr) + sizeof(struct udphdr));
+			   amt_ip_hlen(amt) + sizeof(struct udphdr));
 	if (err)
 		return true;
 
 	skb_reset_inner_headers(skb);
-	memset(&fl4, 0, sizeof(struct flowi4));
-	fl4.flowi4_oif         = amt->stream_dev->ifindex;
-	fl4.daddr              = tunnel->addr.ip4;
-	fl4.saddr              = amt->local_ip;
-	fl4.flowi4_dscp        = inet_dsfield_to_dscp(AMT_TOS);
-	fl4.flowi4_proto       = IPPROTO_UDP;
-	rt = ip_route_output_key(amt->net, &fl4);
-	if (IS_ERR(rt)) {
-		netdev_dbg(amt->dev, "no route to %pI4\n", &tunnel->addr.ip4);
-		return true;
-	}
-
 	amtmq		= skb_push(skb, sizeof(*amtmq));
 	amtmq->version	= 0;
 	amtmq->type	= AMT_MSG_MEMBERSHIP_QUERY;
@@ -1270,17 +1320,9 @@ static bool amt_send_membership_query(struct amt_dev *amt,
 		skb_set_inner_protocol(skb, htons(ETH_P_IP));
 	else
 		skb_set_inner_protocol(skb, htons(ETH_P_IPV6));
-	udp_tunnel_xmit_skb(rt, sk, skb,
-			    fl4.saddr,
-			    fl4.daddr,
-			    AMT_TOS,
-			    ip4_dst_hoplimit(&rt->dst),
-			    0,
-			    amt->relay_port,
-			    tunnel->source_port,
-			    false,
-			    false,
-			    0);
+	if (amt_udp_xmit(amt, sk, skb, &tunnel->addr, amt->relay_port,
+			 tunnel->source_port))
+		return true;
 	amt_update_relay_status(tunnel, AMT_STATUS_SENT_QUERY, true);
 	return false;
 }
-- 
2.43.0