ipv6: weaken the v4mapped source check

[ Upstream commit dcc32f4f183ab8479041b23a1525d48233df1d43 ]

This reverts commit 6af1799aaf3f1bc8defedddfa00df3192445bbf3.

Commit 6af1799aaf3f ("ipv6: drop incoming packets having a v4mapped
source address") introduced an input check against v4mapped addresses.
Use of such addresses on the wire is indeed questionable and not
allowed on public Internet. As the commit pointed out

  https://tools.ietf.org/html/draft-itojun-v6ops-v4mapped-harmful-02

lists potential issues.

Unfortunately there are applications which use v4mapped addresses,
and breaking them is a clear regression. For example v4mapped
addresses (or any semi-valid addresses, really) may be used
for uni-direction event streams or packet export.

Since the issue which sparked the addition of the check was with
TCP and request_socks in particular push the check down to TCPv6
and DCCP. This restores the ability to receive UDPv6 packets with
v4mapped address as the source.

Keep using the IPSTATS_MIB_INHDRERRORS statistic to minimize the
user-visible changes.

Fixes: 6af1799aaf3f ("ipv6: drop incoming packets having a v4mapped source address")
Reported-by: Sunyi Shao <sunyishao@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index b438bed6749d47b9103c3c1cea1d1d7056e5c2fc..2cd3508a378692db5f4f23ae3cd32c68821d4d30 100644 (file)
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -319,6 +319,11 @@ static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
        if (!ipv6_unicast_destination(skb))
                return 0;       /* discard, don't send a reset here */
 
+       if (ipv6_addr_v4mapped(&ipv6_hdr(skb)->saddr)) {
+               __IP6_INC_STATS(sock_net(sk), NULL, IPSTATS_MIB_INHDRERRORS);
+               return 0;
+       }
+
        if (dccp_bad_service_code(sk, service)) {
                dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
                goto drop;

diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index acf0749ee5bbdc2cdbbf5f39791cb163e205a638..57d84accbf1e3ee87c2f37cb5f04510fd4d75e14 100644 (file)
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -222,16 +222,6 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
        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);
 

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6e84f2eb08d643c2c79f34e90b05329a3dbabb56..8d822df83b082462dc60f60d0760a46cbd70037a 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1039,6 +1039,11 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
        if (!ipv6_unicast_destination(skb))
                goto drop;
 
+       if (ipv6_addr_v4mapped(&ipv6_hdr(skb)->saddr)) {
+               __IP6_INC_STATS(sock_net(sk), NULL, IPSTATS_MIB_INHDRERRORS);
+               return 0;
+       }
+
        return tcp_conn_request(&tcp6_request_sock_ops,
                                &tcp_request_sock_ipv6_ops, sk, skb);