ipv6: dccp: fix out of bound access in dccp_v6_err()

dccp_v6_err() does not use pskb_may_pull() and might access garbage.

We only need 4 bytes at the beginning of the DCCP header, like TCP,
so the 8 bytes pulled in icmpv6_notify() are more than enough.

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

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 09c4e19aa285ffd4eeab699eb2a59be4340c24b3..b2a43af967e5b150449666cf96cb9a9c2c24eb05 100644 (file)
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -70,7 +70,7 @@ static void dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                        u8 type, u8 code, int offset, __be32 info)
 {
        const struct ipv6hdr *hdr = (const struct ipv6hdr *)skb->data;
-       const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + offset);
+       const struct dccp_hdr *dh;
        struct dccp_sock *dp;
        struct ipv6_pinfo *np;
        struct sock *sk;
@@ -78,12 +78,13 @@ static void dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
        __u64 seq;
        struct net *net = dev_net(skb->dev);
 
-       if (skb->len < offset + sizeof(*dh) ||
-           skb->len < offset + __dccp_basic_hdr_len(dh)) {
-               __ICMP6_INC_STATS(net, __in6_dev_get(skb->dev),
-                                 ICMP6_MIB_INERRORS);
-               return;
-       }
+       /* Only need dccph_dport & dccph_sport which are the first
+        * 4 bytes in dccp header.
+        * Our caller (icmpv6_notify()) already pulled 8 bytes for us.
+        */
+       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_sport) > 8);
+       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_dport) > 8);
+       dh = (struct dccp_hdr *)(skb->data + offset);
 
        sk = __inet6_lookup_established(net, &dccp_hashinfo,
                                        &hdr->daddr, dh->dccph_dport,