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Subject[PATCH 3.8 52/81] ipv6: gre: correct calculation of max_headroom
Date
3.8.13.12 -stable review patch.  If anyone has any objections, please let me know.

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

From: Hannes Frederic Sowa <hannes@stressinduktion.org>

[ Upstream commit 3da812d860755925da890e8c713f2d2e2d7b1bae ]

gre_hlen already accounts for sizeof(struct ipv6_hdr) + gre header,
so initialize max_headroom to zero. Otherwise the

if (encap_limit >= 0) {
max_headroom += 8;
mtu -= 8;
}

increments an uninitialized variable before max_headroom was reset.

Found with coverity: 728539

Cc: Dmitry Kozlov <xeb@mail.ru>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
net/ipv6/ip6_gre.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index a4c5ae7..be42860 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -659,7 +659,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
struct ip6_tnl *tunnel = netdev_priv(dev);
struct net_device *tdev; /* Device to other host */
struct ipv6hdr *ipv6h; /* Our new IP header */
- unsigned int max_headroom; /* The extra header space needed */
+ unsigned int max_headroom = 0; /* The extra header space needed */
int gre_hlen;
struct ipv6_tel_txoption opt;
int mtu;
@@ -733,7 +733,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
tunnel->err_count = 0;
}

- max_headroom = LL_RESERVED_SPACE(tdev) + gre_hlen + dst->header_len;
+ max_headroom += LL_RESERVED_SPACE(tdev) + gre_hlen + dst->header_len;

if (skb_headroom(skb) < max_headroom || skb_shared(skb) ||
(skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
--
1.8.1.2


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