[PATCH 3.16 015/204] ip6_gre: skb_push ipv6hdr before packing the header in ip6gre_header

From: Ben Hutchings
Date: Thu Dec 28 2017 - 13:04:26 EST

3.16.52-rc1 review patch. If anyone has any objections, please let me know.


From: Xin Long <lucien.xin@xxxxxxxxx>

commit 76cc0d3282d4b933fa144fa41fbc5318e0fdca24 upstream.

Now in ip6gre_header before packing the ipv6 header, it skb_push t->hlen
which only includes encap_hlen + tun_hlen. It means greh and inner header
would be over written by ipv6 stuff and ipv6h might have no chance to set

Jianlin found this issue when using remote any on ip6_gre, the packets he
captured on gre dev are truncated:

22:50:26.210866 Out ethertype IPv6 (0x86dd), length 120: truncated-ip6 -\
8128 bytes missing!(flowlabel 0x92f40, hlim 0, next-header Options (0) \
payload length: 8192) ::1:2000:0 > ::1:0:86dd: HBH [trunc] ip-proto-128 \

It should also skb_push ipv6hdr so that ipv6h points to the right position
to set ipv6 stuff up.

This patch is to skb_push hlen + sizeof(*ipv6h) and also fix some indents
in ip6gre_header.

Fixes: c12b395a4664 ("gre: Support GRE over IPv6")
Reported-by: Jianlin Shi <jishi@xxxxxxxxxx>
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1172,21 +1172,23 @@ static int ip6gre_tunnel_change_mtu(stru

static int ip6gre_header(struct sk_buff *skb, struct net_device *dev,
- unsigned short type,
- const void *daddr, const void *saddr, unsigned int len)
+ unsigned short type, const void *daddr,
+ const void *saddr, unsigned int len)
struct ip6_tnl *t = netdev_priv(dev);
- struct ipv6hdr *ipv6h = (struct ipv6hdr *)skb_push(skb, t->hlen);
- __be16 *p = (__be16 *)(ipv6h+1);
+ struct ipv6hdr *ipv6h;
+ __be16 *p;

+ ipv6h = (struct ipv6hdr *)skb_push(skb, t->hlen + sizeof(*ipv6h));
ip6_flow_hdr(ipv6h, 0, t->fl.u.ip6.flowlabel);
ipv6h->hop_limit = t->parms.hop_limit;
ipv6h->nexthdr = NEXTHDR_GRE;
ipv6h->saddr = t->parms.laddr;
ipv6h->daddr = t->parms.raddr;

- p[0] = t->parms.o_flags;
- p[1] = htons(type);
+ p = (__be16 *)(ipv6h + 1);
+ p[0] = t->parms.o_flags;
+ p[1] = htons(type);

* Set the source hardware address.