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Subject[PATCH 3.2 112/115] ipv6: Count in extension headers in skb->network_header
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jakub Sitnicki <jkbs@redhat.com>

[ Upstream commit 3ba3458fb9c050718b95275a3310b74415e767e2 ]

When sending a UDPv6 message longer than MTU, account for the length
of fragmentable IPv6 extension headers in skb->network_header offset.
Same as we do in alloc_new_skb path in __ip6_append_data().

This ensures that later on __ip6_make_skb() will make space in
headroom for fragmentable extension headers:

/* move skb->data to ip header from ext header */
if (skb->data < skb_network_header(skb))
__skb_pull(skb, skb_network_offset(skb));

Prevents a splat due to skb_under_panic:

skbuff: skb_under_panic: text:ffffffff8143397b len:2126 put:14 \
head:ffff880005bacf50 data:ffff880005bacf4a tail:0x48 end:0xc0 dev:lo
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:104!
invalid opcode: 0000 [#1] KASAN
CPU: 0 PID: 160 Comm: reproducer Not tainted 4.6.0-rc2 #65
[...]
Call Trace:
[<ffffffff813eb7b9>] skb_push+0x79/0x80
[<ffffffff8143397b>] eth_header+0x2b/0x100
[<ffffffff8141e0d0>] neigh_resolve_output+0x210/0x310
[<ffffffff814eab77>] ip6_finish_output2+0x4a7/0x7c0
[<ffffffff814efe3a>] ip6_output+0x16a/0x280
[<ffffffff815440c1>] ip6_local_out+0xb1/0xf0
[<ffffffff814f1115>] ip6_send_skb+0x45/0xd0
[<ffffffff81518836>] udp_v6_send_skb+0x246/0x5d0
[<ffffffff8151985e>] udpv6_sendmsg+0xa6e/0x1090
[...]

Reported-by: Ji Jianwen <jiji@redhat.com>
Signed-off-by: Jakub Sitnicki <jkbs@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv6/ip6_output.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1109,9 +1109,8 @@ static inline int ip6_ufo_append_data(st
int getfrag(void *from, char *to, int offset, int len,
int odd, struct sk_buff *skb),
void *from, int length, int hh_len, int fragheaderlen,
- int transhdrlen, int mtu,unsigned int flags,
- struct rt6_info *rt)
-
+ int exthdrlen, int transhdrlen, int mtu,
+ unsigned int flags, struct rt6_info *rt)
{
struct sk_buff *skb;
int err;
@@ -1136,7 +1135,7 @@ static inline int ip6_ufo_append_data(st
skb_put(skb,fragheaderlen + transhdrlen);

/* initialize network header pointer */
- skb_reset_network_header(skb);
+ skb_set_network_header(skb, exthdrlen);

/* initialize protocol header pointer */
skb->transport_header = skb->network_header + fragheaderlen;
@@ -1342,7 +1341,7 @@ int ip6_append_data(struct sock *sk, int
(rt->dst.dev->features & NETIF_F_UFO) &&
(sk->sk_type == SOCK_DGRAM)) {
err = ip6_ufo_append_data(sk, getfrag, from, length,
- hh_len, fragheaderlen,
+ hh_len, fragheaderlen, exthdrlen,
transhdrlen, mtu, flags, rt);
if (err)
goto error;
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