[PATCH net 2/3] ip6_gre: Make o_seqno start from 0 in native mode

Peilin Ye
2022-04-21T22:08:58Z

For IP6GRE and IP6GRETAP 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 the "if (tunnel->parms.collect_md)" clause in __gre6_xmit(),
where tunnel->o_seqno is passed to gre_build_header() before getting
incremented.

Fixes: c12b395a4664 ("gre: Support GRE over IPv6")
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
---
net/ipv6/ip6_gre.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 976236736146..d9e4ac94eab4 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -724,6 +724,7 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
{
struct ip6_tnl *tunnel = netdev_priv(dev);
__be16 protocol;
+ __be16 flags;

if (dev->type == ARPHRD_ETHER)
IPCB(skb)->flags = 0;
@@ -739,7 +740,6 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
if (tunnel->parms.collect_md) {
struct ip_tunnel_info *tun_info;
const struct ip_tunnel_key *key;
- __be16 flags;
int tun_hlen;

tun_info = skb_tunnel_info_txcheck(skb);
@@ -770,15 +770,14 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
: 0);

} else {
- if (tunnel->parms.o_flags & TUNNEL_SEQ)
- tunnel->o_seqno++;
-
if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen))
return -ENOMEM;

- gre_build_header(skb, tunnel->tun_hlen, tunnel->parms.o_flags,
+ flags = tunnel->parms.o_flags;
+
+ gre_build_header(skb, tunnel->tun_hlen, flags,
protocol, tunnel->parms.o_key,
- htonl(tunnel->o_seqno));
+ (flags & TUNNEL_SEQ) ? htonl(tunnel->o_seqno++) : 0);
}

return ip6_tnl_xmit(skb, dev, dsfield, fl6, encap_limit, pmtu,
--
2.20.1