Sit uses skb->protocol to determine packet type, and bails out if it's
not set. For AF_PACKET injection, we need to support its call chain of:

    packet_sendmsg -> packet_snd -> packet_parse_headers ->
      dev_parse_header_protocol -> parse_protocol

Without a valid parse_protocol, this returns zero, and sit rejects the
skb. So, this wires up the ip_tunnel handler for layer 3 packets for
that case.

Reported-by: Willem de Bruijn <willemdebruijn.ker...@gmail.com>
Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com>
---
 net/ipv6/sit.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 1fbb4dfbb191..5e2c34c0ac97 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1421,6 +1421,7 @@ static void ipip6_tunnel_setup(struct net_device *dev)
        int t_hlen = tunnel->hlen + sizeof(struct iphdr);
 
        dev->netdev_ops         = &ipip6_netdev_ops;
+       dev->header_ops         = &ip_tunnel_header_ops;
        dev->needs_free_netdev  = true;
        dev->priv_destructor    = ipip6_dev_free;
 
-- 
2.27.0

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