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

commit 1aa9d1a0e7eefcc61696e147d123453fc0016005 upstream.

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 86eedbaf037ff2bc18d23bc5c764dd3ba8ae5d2c..e9ce581b9502819a6041c7e1d852ef17b6dff537 100644 (file)
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -83,7 +83,7 @@ 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;
@@ -91,12 +91,13 @@ 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_BH(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(net, &dccp_hashinfo,
                        &hdr->daddr, dh->dccph_dport,