[PATCH 4.9 28/66] ip_gre: Make o_seqno start from 0 in native mode

Greg Kroah-Hartman
2022-05-10T13:20:04Z

From: Peilin Ye <peilin.ye@bytedance.com>

[ 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>
---
net/ipv4/ip_gre.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index fe1801d9f059..eec225c637f0 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -339,14 +339,12 @@ 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);
}
--
2.35.1