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

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Date:   Thu, 21 Apr 2022 15:08:38 -0700
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Peilin Ye <peilin.ye@...edance.com>, "xeb@...l.ru" <xeb@...l.ru>,
        William Tu <u9012063@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Cong Wang <cong.wang@...edance.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peilin Ye <yepeilin.cs@...il.com>
Subject: [PATCH net 2/3] ip6_gre: Make o_seqno start from 0 in native mode

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

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@...edance.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