ip6_tunnel: Fix broken GRO

GRO code checks for matching layer 2 headers to see, if packet belongs
to the same flow and because ip6 tunnel set dev->hard_header_len
this check fails in cases, where it shouldn't. To fix this don't
set hard_header_len, but use needed_headroom like ipv4/ip_tunnel.c
does.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Link: https://patch.msgid.link/20240815151419.109864-1-tbogendoerfer@suse.deSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv6/ip6_tunnel.c

@@ -1507,7 +1507,8 @@ static void ip6_tnl_link_config(struct ip6_tnl *t)
 			tdev = __dev_get_by_index(t->net, p->link);
 
 		if (tdev) {
-			dev->hard_header_len = tdev->hard_header_len + t_hlen;
+			dev->needed_headroom = tdev->hard_header_len +
+				tdev->needed_headroom + t_hlen;
 			mtu = min_t(unsigned int, tdev->mtu, IP6_MAX_MTU);
 
 			mtu = mtu - t_hlen;
@@ -1731,7 +1732,9 @@ ip6_tnl_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
 int ip6_tnl_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct ip6_tnl *tnl = netdev_priv(dev);
+	int t_hlen;
 
+	t_hlen = tnl->hlen + sizeof(struct ipv6hdr);
 	if (tnl->parms.proto == IPPROTO_IPV6) {
 		if (new_mtu < IPV6_MIN_MTU)
 			return -EINVAL;
@@ -1740,10 +1743,10 @@ int ip6_tnl_change_mtu(struct net_device *dev, int new_mtu)
 			return -EINVAL;
 	}
 	if (tnl->parms.proto == IPPROTO_IPV6 || tnl->parms.proto == 0) {
-		if (new_mtu > IP6_MAX_MTU - dev->hard_header_len)
+		if (new_mtu > IP6_MAX_MTU - dev->hard_header_len - t_hlen)
 			return -EINVAL;
 	} else {
-		if (new_mtu > IP_MAX_MTU - dev->hard_header_len)
+		if (new_mtu > IP_MAX_MTU - dev->hard_header_len - t_hlen)
 			return -EINVAL;
 	}
 	WRITE_ONCE(dev->mtu, new_mtu);
@@ -1887,12 +1890,11 @@ ip6_tnl_dev_init_gen(struct net_device *dev)
 	t_hlen = t->hlen + sizeof(struct ipv6hdr);
 
 	dev->type = ARPHRD_TUNNEL6;
-	dev->hard_header_len = LL_MAX_HEADER + t_hlen;
 	dev->mtu = ETH_DATA_LEN - t_hlen;
 	if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
 		dev->mtu -= 8;
 	dev->min_mtu = ETH_MIN_MTU;
-	dev->max_mtu = IP6_MAX_MTU - dev->hard_header_len;
+	dev->max_mtu = IP6_MAX_MTU - dev->hard_header_len - t_hlen;
 
 	netdev_hold(dev, &t->dev_tracker, GFP_KERNEL);
 	netdev_lockdep_set_classes(dev);