ah: reload pointers to skb data after calling skb_cow_data()

skb_cow_data() may allocate a new data buffer, so pointers on
skb should be set after this function.

Bug was introduced by commit dff3bb06 ("ah4: convert to ahash")
and 8631e9bd ("ah6: convert to ahash").

Signed-off-by: Wang Xuefu <xuefu.wang@6wind.com>
Acked-by: Krzysztof Witek <krzysztof.witek@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index 880a5ec6dce0..86961bec70ab 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -314,14 +314,15 @@ static int ah_input(struct xfrm_state *x, struct sk_buff *skb)
 
         skb->ip_summed = CHECKSUM_NONE;
 
-        ah = (struct ip_auth_hdr *)skb->data;
-        iph = ip_hdr(skb);
-        ihl = ip_hdrlen(skb);
 
         if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
                 goto out;
         nfrags = err;
 
+        ah = (struct ip_auth_hdr *)skb->data;
+        iph = ip_hdr(skb);
+        ihl = ip_hdrlen(skb);
+
         work_iph = ah_alloc_tmp(ahash, nfrags, ihl + ahp->icv_trunc_len);
         if (!work_iph)
                 goto out;