fix

Makefile

@@ -10,6 +10,11 @@ all: module tools
 module:
 	$(MAKE) -C $(KDIR) M=$(PWD) modules
 
+tools: etherip6ctl
+
+etherip6ctl: etherip6ctl.c etherip6_uapi.h
+	$(CC) $(CFLAGS) -Wall -Wextra -O2 -o $@ etherip6ctl.c
+
 clean:
 	@if [ -d "$(KDIR)" ]; then \
 		$(MAKE) -C "$(KDIR)" M="$(PWD)" clean; \

README.md

@@ -37,9 +37,13 @@ sudo ip link set eip0 up
 sudo ip addr add 192.0.2.1/30 dev eip0
 ```
 
-TCP SYN に MSS オプションがある場合、外側 IPv6 経路の MTU を超えないよう、
+Overlay MTUのデフォルトは1500です。Underlayの経路MTUも1500の場合、
-送信時に IPv4/IPv6 の MSS を自動的に縮小します。802.1Q/802.1ad VLAN と IPv6
+カプセル化後の外側IPv6パケットはMTUを超えるため、送信元で経路MTU以下の
-拡張ヘッダーにも対応します。既に十分小さい MSS は変更しません。
+IPv6フラグメントに分割します。
+
+```sh
+sudo ip link set eip0 mtu 1500
+```
 
 ## トンネルの削除
 

etherip6.c

@@ -5,7 +5,6 @@
 #include <linux/in6.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
-#include <linux/if_vlan.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/module.h>
@@ -15,17 +14,12 @@
 #include <linux/rculist.h>
 #include <linux/rtnetlink.h>
 #include <linux/skbuff.h>
-#include <linux/tcp.h>
-#include <linux/unaligned.h>
-#include <net/checksum.h>
-#include <net/ip.h>
 #include <net/ip6_route.h>
 #include <net/ipv6.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <net/protocol.h>
 #include <net/rtnetlink.h>
-#include <net/tcp.h>
 
 #include "etherip6_uapi.h"
 
@@ -38,9 +32,7 @@
 #define ETHERIP6_HLEN 2
 #define ETHERIP6_DEFAULT_HOP_LIMIT 64
 #define ETHERIP6_MAX_MTU 9000
-
+#define ETHERIP6_ENCAP_HLEN (sizeof(struct ipv6hdr) + ETHERIP6_HLEN)
-/* IPv6 + EtherIP headers added outside the encapsulated Ethernet frame. */
-#define ETHERIP6_OUTER_HLEN (sizeof(struct ipv6hdr) + ETHERIP6_HLEN)
 
 struct etherip6_tunnel {
 	struct list_head list;
@@ -149,110 +141,6 @@ static struct etherip6_tunnel *etherip6_lookup_rx(struct net *net,
 	return etherip6_lookup_unique_rx(net, local, remote, iif, false, false);
 }
 
-static void etherip6_clamp_tcp_mss(struct sk_buff *skb, unsigned int path_mtu)
-{
-	struct vlan_hdr _vh, *vh;
-	struct tcphdr _th, *th;
-	struct ethhdr _eth, *eth;
-	unsigned int nhoff = ETH_HLEN;
-	unsigned int thoff, tcp_hlen;
-	unsigned int inner_mtu;
-	unsigned int min_ip_hlen;
-	unsigned char *opt;
-	unsigned int optlen;
-	__be16 proto;
-	u16 old_mss, new_mss;
-	u8 nexthdr;
-
-	eth = skb_header_pointer(skb, 0, sizeof(_eth), &_eth);
-	if (!eth)
-		return;
-	proto = eth->h_proto;
-
-	while (eth_type_vlan(proto)) {
-		vh = skb_header_pointer(skb, nhoff, sizeof(_vh), &_vh);
-		if (!vh)
-			return;
-		proto = vh->h_vlan_encapsulated_proto;
-		nhoff += sizeof(*vh);
-	}
-
-	if (path_mtu <= ETHERIP6_OUTER_HLEN + nhoff)
-		return;
-	inner_mtu = min_t(unsigned int, skb->dev->mtu,
-			  path_mtu - ETHERIP6_OUTER_HLEN - nhoff);
-
-	if (proto == htons(ETH_P_IP)) {
-		struct iphdr _iph, *iph;
-
-		iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
-		if (!iph || iph->version != 4 || iph->ihl < 5 ||
-		    iph->protocol != IPPROTO_TCP ||
-		    (iph->frag_off & htons(IP_MF | IP_OFFSET)))
-			return;
-		thoff = nhoff + iph->ihl * 4;
-		min_ip_hlen = sizeof(struct iphdr);
-	} else if (proto == htons(ETH_P_IPV6)) {
-		struct ipv6hdr _ip6h, *ip6h;
-		__be16 frag_off = 0;
-		int offset;
-
-		ip6h = skb_header_pointer(skb, nhoff, sizeof(_ip6h), &_ip6h);
-		if (!ip6h || ip6h->version != 6)
-			return;
-		nexthdr = ip6h->nexthdr;
-		offset = ipv6_skip_exthdr(skb, nhoff + sizeof(*ip6h),
-				     &nexthdr, &frag_off);
-		if (offset < 0 || nexthdr != IPPROTO_TCP || frag_off)
-			return;
-		thoff = offset;
-		min_ip_hlen = sizeof(struct ipv6hdr);
-	} else {
-		return;
-	}
-
-	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
-	if (!th || !th->syn || th->doff < sizeof(*th) / 4)
-		return;
-	tcp_hlen = th->doff * 4;
-	if (inner_mtu <= min_ip_hlen + sizeof(*th))
-		return;
-	new_mss = min_t(unsigned int, U16_MAX,
-			inner_mtu - min_ip_hlen - sizeof(*th));
-
-	if (skb_ensure_writable(skb, thoff + tcp_hlen))
-		return;
-	th = (struct tcphdr *)(skb->data + thoff);
-	opt = (unsigned char *)(th + 1);
-	optlen = tcp_hlen - sizeof(*th);
-
-	while (optlen) {
-		u8 kind = opt[0];
-		u8 len;
-
-		if (kind == TCPOPT_EOL)
-			return;
-		if (kind == TCPOPT_NOP) {
-			opt++;
-			optlen--;
-			continue;
-		}
-		if (optlen < 2 || (len = opt[1]) < 2 || len > optlen)
-			return;
-		if (kind == TCPOPT_MSS && len == TCPOLEN_MSS) {
-			old_mss = get_unaligned_be16(opt + 2);
-			if (old_mss > new_mss) {
-				put_unaligned_be16(new_mss, opt + 2);
-				inet_proto_csum_replace2(&th->check, skb,
-						 htons(old_mss), htons(new_mss), false);
-			}
-			return;
-		}
-		opt += len;
-		optlen -= len;
-	}
-}
-
 static netdev_tx_t etherip6_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct etherip6_tunnel *tun = netdev_priv(dev);
@@ -280,8 +168,6 @@ static netdev_tx_t etherip6_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto tx_error;
 	}
 
-	etherip6_clamp_tcp_mss(skb, dst_mtu(dst));
-
 	headroom = LL_RESERVED_SPACE(dst->dev) + sizeof(*ip6h) + ETHERIP6_HLEN;
 	err = skb_cow_head(skb, headroom);
 	if (err) {
@@ -306,18 +192,17 @@ static netdev_tx_t etherip6_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->dev = dst->dev;
+	/*
+	 * This skb used to contain an inner Ethernet frame.  Clear its control
+	 * block before handing it to IPv6, then pin source fragmentation to the
+	 * current underlay PMTU.  ip6_local_out() adds the Fragment Header and
+	 * splits oversized packets in ip6_finish_output().
+	 */
+	memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+	IP6CB(skb)->frag_max_size = dst_mtu(dst);
 	skb->ignore_df = 1;
 	skb_dst_set(skb, dst);
 
-	/*
-	 * skb->cb belongs to the protocol currently processing the skb.  The
-	 * encapsulated frame may leave bridge, qdisc, or inner IPv6 state in it;
-	 * in particular, stale inet6_skb_parm flags or frag_max_size corrupt the
-	 * outer IPv6 fragmentation path.  Native IPv6 tunnels clear this state
-	 * in ip6tunnel_xmit() before calling ip6_local_out().
-	 */
-	memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
-
 	stats = this_cpu_ptr(tun->stats);
 	u64_stats_update_begin(&stats->syncp);
 	u64_stats_inc(&stats->tx_packets);
@@ -376,6 +261,7 @@ static void etherip6_setup(struct net_device *dev)
 	dev->vlan_features = 0;
 	dev->min_mtu = ETH_MIN_MTU;
 	dev->max_mtu = ETHERIP6_MAX_MTU;
+	dev->needed_headroom = ETHERIP6_ENCAP_HLEN;
 	eth_hw_addr_random(dev);
 }