xfrm6: fix a potential use after free in xfrm6_policy.c

pskb_may_pull() maybe change skb->data and make nh and exthdr pointer
oboslete, so recompute the nd and exthdr

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
index ac49f84..5f98364 100644 (file)
--- a/net/ipv6/xfrm6_policy.c
+++ b/net/ipv6/xfrm6_policy.c
@@ -170,8 +170,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
                case IPPROTO_DCCP:
                        if (!onlyproto && (nh + offset + 4 < skb->data ||
                             pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
-                               __be16 *ports = (__be16 *)exthdr;
+                               __be16 *ports;
 
+                               nh = skb_network_header(skb);
+                               ports = (__be16 *)(nh + offset);
                                fl6->fl6_sport = ports[!!reverse];
                                fl6->fl6_dport = ports[!reverse];
                        }
@@ -180,8 +182,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 
                case IPPROTO_ICMPV6:
                        if (!onlyproto && pskb_may_pull(skb, nh + offset + 2 - skb->data)) {
-                               u8 *icmp = (u8 *)exthdr;
+                               u8 *icmp;
 
+                               nh = skb_network_header(skb);
+                               icmp = (u8 *)(nh + offset);
                                fl6->fl6_icmp_type = icmp[0];
                                fl6->fl6_icmp_code = icmp[1];
                        }
@@ -192,8 +196,9 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
                case IPPROTO_MH:
                        if (!onlyproto && pskb_may_pull(skb, nh + offset + 3 - skb->data)) {
                                struct ip6_mh *mh;
-                               mh = (struct ip6_mh *)exthdr;
 
+                               nh = skb_network_header(skb);
+                               mh = (struct ip6_mh *)(nh + offset);
                                fl6->fl6_mh_type = mh->ip6mh_type;
                        }
                        fl6->flowi6_proto = nexthdr;