[PATCH] ipv4: fix a potential use after free in gre_offload.c

[r***@gmail.com]

From: Li RongQing <***@gmail.com>

pskb_may_pull() may change skb->data and make greh pointer oboslete;
so need to reassign greh;
but since first calling pskb_may_pull already ensured that skb->data
has enough space for greh, so move the reference of greh before second
calling pskb_may_pull(), to avoid reassign greh.

Fixes: 7a7ffbabf9("ipv4: fix tunneled VM traffic over hw VXLAN/GRE GSO NIC")
Cc: Wei-Chun Chao <***@plumgrid.com>
Signed-off-by: Li RongQing <***@gmail.com>
---
net/ipv4/gre_offload.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index a777295..ccda096 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -55,13 +55,13 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
if (csum)
skb->encap_hdr_csum = 1;

- if (unlikely(!pskb_may_pull(skb, ghl)))
- goto out;
-
/* setup inner skb. */
skb->protocol = greh->protocol;
skb->encapsulation = 0;

+ if (unlikely(!pskb_may_pull(skb, ghl)))
+ goto out;
+
__skb_pull(skb, ghl);
skb_reset_mac_header(skb);
skb_set_network_header(skb, skb_inner_network_offset(skb));

[Eric Dumazet]

Post by r***@gmail.com
pskb_may_pull() may change skb->data and make greh pointer oboslete;
so need to reassign greh;
but since first calling pskb_may_pull already ensured that skb->data
has enough space for greh, so move the reference of greh before second
calling pskb_may_pull(), to avoid reassign greh.
Fixes: 7a7ffbabf9("ipv4: fix tunneled VM traffic over hw VXLAN/GRE GSO NIC")
---

Acked-by: Eric Dumazet <***@google.com>

[David Miller]

From: ***@gmail.com
Date: Sat, 18 Oct 2014 17:26:04 +0800

Post by r***@gmail.com
pskb_may_pull() may change skb->data and make greh pointer oboslete;
so need to reassign greh;
but since first calling pskb_may_pull already ensured that skb->data
has enough space for greh, so move the reference of greh before second
calling pskb_may_pull(), to avoid reassign greh.
Fixes: 7a7ffbabf9("ipv4: fix tunneled VM traffic over hw VXLAN/GRE GSO NIC")

Applied.