Am 12.11.17 um 10:32 schrieb Antonio Quartulli:
> Hi,
>
> On 12/11/17 00:07, Arne Schwabe wrote:
>> This can be used to redirect all IPv6 traffic to the tun interface,
>> effectively black holing the IPv6 traffic. Without ICMPv6 error messages
>> this will result in timeouts when the server does not send error codes.
>> block-ipv6 allows client side only blocking on all platforms that OpenVPN
>> supports IPv6. On Android it is only way to do sensible IPv6 blocking on
>> Android < 5.0 and broken devices (Samsung).
>> ---
>> doc/openvpn.8 | 17 +++++
>> src/openvpn/forward.c | 170
>> ++++++++++++++++++++++++++++++++++++++++++++++++--
>> src/openvpn/forward.h | 3 +-
>> src/openvpn/misc.c | 4 +-
>> src/openvpn/options.c | 17 +++++
>> src/openvpn/options.h | 1 +
>> src/openvpn/proto.h | 19 ++++++
>> 7 files changed, 224 insertions(+), 7 deletions(-)
>>
>> diff --git a/doc/openvpn.8 b/doc/openvpn.8
>> index a4189ac2..26b5f7de 100644
>> --- a/doc/openvpn.8
>> +++ b/doc/openvpn.8
>> @@ -1232,6 +1232,23 @@ Like \-\-redirect\-gateway, but omit actually
>> changing the default
>> gateway. Useful when pushing private subnets.
>> .\"*********************************************************
>> .TP
>> +.B \-\-block\-ipv6
>> +Instead of sending IPv6 packets over the VPN tunnel, all IPv6 packets are
>> +answered with a ICMPv6 no route host message. This options is intended for
>> +cases when IPv6 should be blocked and other options are not available.
>> +
>> +Following config block would send all IPv6 traffic to OpenVPN and answer all
>> +requests with no route to host, effectively blocking IPv6.
>> +
>> +.B \-\-ifconfig-ipv6
>> +fd15:53b6:dead::2/64 fd15:53b6:dead::1
>> +.br
>> +.B \-\-redirect\-gateway
>> +ipv6
>> +.br
>> +.B \-\-block\-ipv6
>> +.\"*********************************************************
>> +.TP
>> .B \-\-tun\-mtu n
>> Take the TUN device MTU to be
>> .B n
>> diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
>> index 1b7455bb..21cce90b 100644
>> --- a/src/openvpn/forward.c
>> +++ b/src/openvpn/forward.c
>> @@ -1198,7 +1198,7 @@ process_incoming_tun(struct context *c)
>> * The --passtos and --mssfix options require
>> * us to examine the IP header (IPv4 or IPv6).
>> */
>> - process_ip_header(c, PIPV4_PASSTOS|PIP_MSSFIX|PIPV4_CLIENT_NAT,
>> &c->c2.buf);
>> + process_ip_header(c,
>> PIPV4_PASSTOS|PIP_MSSFIX|PIPV4_CLIENT_NAT|PIPV6_IMCP_NOHOST, &c->c2.buf);
>>
>> #ifdef PACKET_TRUNCATION_CHECK
>> /* if (c->c2.buf.len > 1) --c->c2.buf.len; */
>> @@ -1209,6 +1209,9 @@ process_incoming_tun(struct context *c)
>> &c->c2.n_trunc_pre_encrypt);
>> #endif
>>
>> + }
>> + if (c->c2.buf.len > 0)
>> + {
>> encrypt_sign(c, true);
>> }
>
> I might not have a full understanding of this chunk: but could you
> explain how this is related to this patch?
It is similar to what check_ping_send_dowork does. Since you create a
new packet that goes out that is in the buf, it needs to be encryped and
signed.
>> +
>> + /* IPv6 Header */
>> + ASSERT(buf_write_prepend(&c->c2.to_tun, &pip6out, sizeof(struct
>> openvpn_ipv6hdr)));
>> +
>
> I see lots of asserts here and in other functions below.
>
> Is it possible that a bridged/routed client could send a malformed IPv6
> packet to convert this ASSERTs into a DoS for the VPN client?
No, should not be, it is basically only to make sure the buf functions
return true.
>
> Actually, any chance that this function is executed on the server? or is
> this impossible?
I will test, should be possible.
Arne
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