3.16.80-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit 6af1799aaf3f1bc8defedddfa00df3192445bbf3 upstream.
This began with a syzbot report. syzkaller was injecting IPv6 TCP SYN packets having a v4mapped source address.
After an unsuccessful 4-tuple lookup, TCP creates a request socket (SYN_RECV) and calls reqsk_queue_hash_req()
reqsk_queue_hash_req() calls sk_ehashfn(sk)
At this point we have AF_INET6 sockets, and the heuristic used by sk_ehashfn() to either hash the IPv4 or IPv6 addresses is to use ipv6_addr_v4mapped(&sk->sk_v6_daddr)
For the particular spoofed packet, we end up hashing V4 addresses which were not initialized by the TCP IPv6 stack, so KMSAN fired a warning.
I first fixed sk_ehashfn() to test both source and destination addresses, but then faced various problems, including user-space programs like packetdrill that had similar assumptions.
Instead of trying to fix the whole ecosystem, it is better to admit that we have a dual stack behavior, and that we can not build linux kernels without V4 stack anyway.
The dual stack API automatically forces the traffic to be IPv4 if v4mapped addresses are used at bind() or connect(), so it makes no sense to allow IPv6 traffic to use the same v4mapped class.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet edumazet@google.com Cc: Florian Westphal fw@strlen.de Cc: Hannes Frederic Sowa hannes@stressinduktion.org Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/ipv6/ip6_input.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/net/ipv6/ip6_input.c +++ b/net/ipv6/ip6_input.c @@ -151,6 +151,16 @@ int ipv6_rcv(struct sk_buff *skb, struct if (ipv6_addr_is_multicast(&hdr->saddr)) goto err;
+ /* While RFC4291 is not explicit about v4mapped addresses + * in IPv6 headers, it seems clear linux dual-stack + * model can not deal properly with these. + * Security models could be fooled by ::ffff:127.0.0.1 for example. + * + * https://tools.ietf.org/html/draft-itojun-v6ops-v4mapped-harmful-02 + */ + if (ipv6_addr_v4mapped(&hdr->saddr)) + goto err; + skb->transport_header = skb->network_header + sizeof(*hdr); IP6CB(skb)->nhoff = offsetof(struct ipv6hdr, nexthdr);