ipv6: mip6: fix mip6_mh_filter()

mip6_mh_filter() should not modify its input, or else its caller
would need to recompute ipv6_hdr() if skb->head is reallocated.

Use skb_header_pointer() instead of pskb_may_pull()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 9 deletions

diff --git a/net/ipv6/mip6.c b/net/ipv6/mip6.c
index 5b087c31d87b..0f9bdc5ee9f3 100644
--- a/net/ipv6/mip6.c
+++ b/net/ipv6/mip6.c
@@ -86,28 +86,30 @@ static int mip6_mh_len(int type)
 
 static int mip6_mh_filter(struct sock *sk, struct sk_buff *skb)
 {
-        struct ip6_mh *mh;
+        struct ip6_mh _hdr;
+        const struct ip6_mh *mh;
 
-        if (!pskb_may_pull(skb, (skb_transport_offset(skb)) + 8) ||
-            !pskb_may_pull(skb, (skb_transport_offset(skb) +
-                                 ((skb_transport_header(skb)[1] + 1) << 3))))
+        mh = skb_header_pointer(skb, skb_transport_offset(skb),
+                                sizeof(_hdr), &_hdr);
+        if (!mh)
                 return -1;
 
-        mh = (struct ip6_mh *)skb_transport_header(skb);
+        if (((mh->ip6mh_hdrlen + 1) << 3) > skb->len)
+                return -1;
 
         if (mh->ip6mh_hdrlen < mip6_mh_len(mh->ip6mh_type)) {
                 LIMIT_NETDEBUG(KERN_DEBUG "mip6: MH message too short: %d vs >=%d\n",
                                mh->ip6mh_hdrlen, mip6_mh_len(mh->ip6mh_type));
-                mip6_param_prob(skb, 0, ((&mh->ip6mh_hdrlen) -
-                                         skb_network_header(skb)));
+                mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_hdrlen) +
+                                skb_network_header_len(skb));
                 return -1;
         }
 
         if (mh->ip6mh_proto != IPPROTO_NONE) {
                 LIMIT_NETDEBUG(KERN_DEBUG "mip6: MH invalid payload proto = %d\n",
                                mh->ip6mh_proto);
-                mip6_param_prob(skb, 0, ((&mh->ip6mh_proto) -
-                                         skb_network_header(skb)));
+                mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_proto) +
+                                skb_network_header_len(skb));
                 return -1;
         }