ipv6: ip6_sk_dst_check() must not assume ipv6 dst

It's possible to use AF_INET6 sockets and to connect to an IPv4
destination. After this, socket dst cache is a pointer to a rtable,
not rt6_info.

ip6_sk_dst_check() should check the socket dst cache is IPv6, or else
various corruptions/crashes can happen.

Dave Jones can reproduce immediate crash with
trinity -q -l off -n -c sendmsg -c connect

With help from Hannes Frederic Sowa

Reported-by: Dave Jones <davej@redhat.com>
Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 95703ba2c084..d5d20cde8d92 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -821,11 +821,17 @@ static struct dst_entry *ip6_sk_dst_check(struct sock *sk,
                                           const struct flowi6 *fl6)
 {
         struct ipv6_pinfo *np = inet6_sk(sk);
-        struct rt6_info *rt = (struct rt6_info *)dst;
+        struct rt6_info *rt;
 
         if (!dst)
                 goto out;
 
+        if (dst->ops->family != AF_INET6) {
+                dst_release(dst);
+                return NULL;
+        }
+
+        rt = (struct rt6_info *)dst;
         /* Yes, checking route validity in not connected
          * case is not very simple. Take into account,
          * that we do not support routing by source, TOS,