- if (pskb_may_pull(skb, xprth + 12 - skb->data)) {
- __be16 *greflags = (__be16 *)xprth;
- __be32 *gre_hdr = (__be32 *)xprth;
+ if (xprth + 12 < skb->data ||
+ pskb_may_pull(skb, xprth + 12 - skb->data)) {
+ __be16 *greflags;
+ __be32 *gre_hdr;
+
+ xprth = skb_network_header(skb) + iph->ihl * 4;
+ greflags = (__be16 *)xprth;
+ gre_hdr = (__be32 *)xprth;