ip_gre: Make o_seqno start from 0 in native mode

[ Upstream commit ff827beb706ed719c766acf36449801ded0c17fc ]

For GRE and GRETAP devices, currently o_seqno starts from 1 in native
mode.  According to RFC 2890 2.2., "The first datagram is sent with a
sequence number of 0."  Fix it.

It is worth mentioning that o_seqno already starts from 0 in collect_md
mode, see gre_fb_xmit(), where tunnel->o_seqno is passed to
gre_build_header() before getting incremented.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 1a4d89f8361cb5dff5d91618c97f29fd40dc4c69..d916accd9783163377eeed10dea9919990793123 100644 (file)
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -429,14 +429,12 @@ static void __gre_xmit(struct sk_buff *skb, struct net_device *dev,
                       __be16 proto)
 {
        struct ip_tunnel *tunnel = netdev_priv(dev);
-
-       if (tunnel->parms.o_flags & TUNNEL_SEQ)
-               tunnel->o_seqno++;
+       __be16 flags = tunnel->parms.o_flags;
 
        /* Push GRE header. */
        gre_build_header(skb, tunnel->tun_hlen,
-                        tunnel->parms.o_flags, proto, tunnel->parms.o_key,
-                        htonl(tunnel->o_seqno));
+                        flags, proto, tunnel->parms.o_key,
+                        (flags & TUNNEL_SEQ) ? htonl(tunnel->o_seqno++) : 0);
 
        ip_tunnel_xmit(skb, dev, tnl_params, tnl_params->protocol);
 }