linux-kernel - [PATCH 3.16 014/136] ipv6: drop incoming packets having a v4mapped source address

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 17 Dec 2019 00:45:48 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Hannes Frederic Sowa" <hannes@...essinduktion.org>,
        "syzbot" <syzkaller@...glegroups.com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Florian Westphal" <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 014/136] ipv6: drop incoming packets having a
 v4mapped source address

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.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@...gle.com>
Cc: Florian Westphal <fw@...len.de>
Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.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);