xfrm6: fix the proto and ports decode of sctp protocol

The SCTP pushed the skb above the sctp chunk header, so the
check of pskb_may_pull(skb, nh + offset + 1 - skb->data) in
_decode_session6() will never return 0 and the ports decode
of sctp will always fail. (nh + offset + 1 - skb->data < 0)

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
index b4b16a43f277..3a3c677bc0f2 100644
--- a/net/ipv6/xfrm6_policy.c
+++ b/net/ipv6/xfrm6_policy.c
@@ -157,7 +157,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
         ipv6_addr_copy(&fl->fl6_dst, reverse ? &hdr->saddr : &hdr->daddr);
         ipv6_addr_copy(&fl->fl6_src, reverse ? &hdr->daddr : &hdr->saddr);
 
-        while (pskb_may_pull(skb, nh + offset + 1 - skb->data)) {
+        while (nh + offset + 1 < skb->data ||
+               pskb_may_pull(skb, nh + offset + 1 - skb->data)) {
                 nh = skb_network_header(skb);
                 exthdr = (struct ipv6_opt_hdr *)(nh + offset);
 
@@ -177,7 +178,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
                 case IPPROTO_TCP:
                 case IPPROTO_SCTP:
                 case IPPROTO_DCCP:
-                        if (!onlyproto && pskb_may_pull(skb, nh + offset + 4 - skb->data)) {
+                        if (!onlyproto && (nh + offset + 4 < skb->data ||
+                             pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
                                 __be16 *ports = (__be16 *)exthdr;
 
                                 fl->fl_ip_sport = ports[!!reverse];