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From 113ab386c7d6625cff284fb10952ff69a58c18a4 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 14 Oct 2011 04:57:46 +0000
Subject: [PATCH] ip_gre: dont increase dev->needed_headroom on a live device
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

It seems ip_gre is able to change dev->needed_headroom on the fly.

Its is not legal unfortunately and triggers a BUG in raw_sendmsg()

skb = sock_alloc_send_skb(sk, ... + LL_ALLOCATED_SPACE(rt->dst.dev)

< another cpu change dev->needed_headromm (making it bigger)

...
skb_reserve(skb, LL_RESERVED_SPACE(rt->dst.dev));

We end with LL_RESERVED_SPACE() being bigger than LL_ALLOCATED_SPACE()
-> we crash later because skb head is exhausted.

Bug introduced in commit 243aad83 in 2.6.34 (ip_gre: include route
header_len in max_headroom calculation)

Reported-by: Elmar Vonlanthen <evonlanthen@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Timo Teräs <timo.teras@iki.fi>
CC: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/ipv4/ip_gre.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index d7bb94c..d55110e 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -835,8 +835,6 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 	if (skb_headroom(skb) < max_headroom || skb_shared(skb)||
 	    (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
 		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
-		if (max_headroom > dev->needed_headroom)
-			dev->needed_headroom = max_headroom;
 		if (!new_skb) {
 			ip_rt_put(rt);
 			dev->stats.tx_dropped++;
-- 
1.7.7