linux-kernel - [PATCH 3.2 112/115] ipv6: Count in extension headers in skb->network

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Message-ID: <lsq.1461711744.29929570@decadent.org.uk>
Date:	Wed, 27 Apr 2016 01:02:24 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
	"Jakub Sitnicki" <jkbs@...hat.com>, "Ji Jianwen" <jiji@...hat.com>,
	"Hannes Frederic Sowa" <hannes@...essinduktion.org>
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@...hat.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@...hat.com>
Signed-off-by: Jakub Sitnicki <jkbs@...hat.com>
Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.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;