[PATCH net 1/5] net: ip_tunnel: add header_ops for layer 3 devices

[Jason A. Donenfeld]

Some devices that take straight up layer 3 packets benefit from having a
shared header_ops so that AF_PACKET sockets can inject packets that are
recognized. This shared infrastructure will be used by other drivers
that currently can't inject packets using AF_PACKET. It also exposes the
parser function, as it is useful in standalone form too.

Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com>
---
 include/net/ip_tunnels.h  |  3 +++
 net/ipv4/ip_tunnel_core.c | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index 076e5d7db7d3..36025dea7612 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -290,6 +290,9 @@ int ip_tunnel_newlink(struct net_device *dev, struct nlattr 
*tb[],
                      struct ip_tunnel_parm *p, __u32 fwmark);
 void ip_tunnel_setup(struct net_device *dev, unsigned int net_id);
 
+extern const struct header_ops ip_tunnel_header_ops;
+__be16 ip_tunnel_parse_protocol(const struct sk_buff *skb);
+
 struct ip_tunnel_encap_ops {
        size_t (*encap_hlen)(struct ip_tunnel_encap *e);
        int (*build_header)(struct sk_buff *skb, struct ip_tunnel_encap *e,
diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index 181b7a2a0247..07d958aa03f8 100644
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2013 Nicira, Inc.
+ * Copyright (C) 2020 Jason A. Donenfeld <ja...@zx2c4.com>. All Rights 
Reserved.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -844,3 +845,21 @@ void ip_tunnel_unneed_metadata(void)
        static_branch_dec(&ip_tunnel_metadata_cnt);
 }
 EXPORT_SYMBOL_GPL(ip_tunnel_unneed_metadata);
+
+/* Returns either the correct skb->protocol value, or 0 if invalid. */
+__be16 ip_tunnel_parse_protocol(const struct sk_buff *skb)
+{
+       if (skb_network_header(skb) >= skb->head &&
+           (skb_network_header(skb) + sizeof(struct iphdr)) <= 
skb_tail_pointer(skb) &&
+           ip_hdr(skb)->version == 4)
+               return htons(ETH_P_IP);
+       if (skb_network_header(skb) >= skb->head &&
+           (skb_network_header(skb) + sizeof(struct ipv6hdr)) <= 
skb_tail_pointer(skb) &&
+           ipv6_hdr(skb)->version == 6)
+               return htons(ETH_P_IPV6);
+       return 0;
+}
+EXPORT_SYMBOL(ip_tunnel_parse_protocol);
+
+const struct header_ops ip_tunnel_header_ops = { .parse_protocol = 
ip_tunnel_parse_protocol };
+EXPORT_SYMBOL(ip_tunnel_header_ops);
-- 
2.27.0