Disable IPv4-mapped - enforce IPV6_V6ONLY

Disable IPv4-mapped - enforce IPV6_V6ONLY

[Alexander Holler]

Hello,

I'm searching for a way to either enforce IPV6_V6ONLY or to block 
IPv4-mapped addresses on ipv6-sockets (e.g. by using iptables) system-wide.

E.g. net.ipv6.bindv6only doesn't help if something calls

int v6on = 0;
setsockopt(sd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&v6on, sizeof(v6on))

In such a case I still want to disable or block IPv4-mapped addresses on 
that socket, even if the program thinks it nows it better.

Until now I haven't found a solution.

Regards,

Alexander

Re: Disable IPv4-mapped - enforce IPV6_V6ONLY

[Alexander Holler]

Am 22.02.2013 16:21, schrieb Alexander Holler:
> Hello,
>
> I'm searching for a way to either enforce IPV6_V6ONLY or to block
> IPv4-mapped addresses on ipv6-sockets (e.g. by using iptables) system-wide.
>
> E.g. net.ipv6.bindv6only doesn't help if something calls
>
> int v6on = 0;
> setsockopt(sd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&v6on, sizeof(v6on))
>
> In such a case I still want to disable or block IPv4-mapped addresses on
> that socket, even if the program thinks it nows it better.
>
> Until now I haven't found a solution.

I've now done it by the following hack:

-----------
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index d1e2e8e..9eefd3e 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -235,7 +235,7 @@ static int do_ipv6_setsockopt(struct sock *sk, int 
level, int optname,
                 if (optlen < sizeof(int) ||
                     inet_sk(sk)->inet_num)
                         goto e_inval;
-               np->ipv6only = valbool;
+               np->ipv6only = valbool || net->ipv6.sysctl.bindv6only;
                 retv = 0;
                 break;
-----------

A proper solution would be to either return false if net.ipv6.bindv6only 
is true and optval is false (which would break downward compatibility 
because it wouldn't just be a default and setsockopt might return an 
error) or to introduce a new sysctl variable like 
net.ipv6.bindv6only_enforced_silently. ("silently" because setsockopt() 
wouldn't return an error if net.ipv6.bindv6only is true and optval 
(v6only in the example above) is false.)

I would volunteer to write a patch which introduces something like 
net.ipv6.bindv6only_enforced_silently if some maintainer would give me 
his ok.

If so, the question remains if

systemctl net.ipv6.bindv6only_enforced_silently = 1

should set systemctl.net.ipv6.bindv6only too or if an error should be 
returned if net.ipv6.bindv6only is false.

Regards,

Alexander

Re: Disable IPv4-mapped - enforce IPV6_V6ONLY

[YOSHIFUJI Hideaki]

Hello.

Alexander Holler wrote:
> Am 22.02.2013 16:21, schrieb Alexander Holler:
>> Hello,
>>
>> I'm searching for a way to either enforce IPV6_V6ONLY or to block
>> IPv4-mapped addresses on ipv6-sockets (e.g. by using iptables) system-wide.
>>
>> E.g. net.ipv6.bindv6only doesn't help if something calls
>>
>> int v6on = 0;
>> setsockopt(sd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&v6on, sizeof(v6on))
>>
>> In such a case I still want to disable or block IPv4-mapped addresses on
>> that socket, even if the program thinks it nows it better.
>>
>> Until now I haven't found a solution.
> 
> I've now done it by the following hack:
> 
> -----------
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index d1e2e8e..9eefd3e 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -235,7 +235,7 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
>                 if (optlen < sizeof(int) ||
>                     inet_sk(sk)->inet_num)
>                         goto e_inval;
> -               np->ipv6only = valbool;
> +               np->ipv6only = valbool || net->ipv6.sysctl.bindv6only;
>                 retv = 0;
>                 break;
> -----------
> 
> A proper solution would be to either return false if net.ipv6.bindv6only is true and optval is false (which would break downward compatibility because it wouldn't just be a default and setsockopt might return an error) or to introduce a new sysctl variable like net.ipv6.bindv6only_enforced_silently. ("silently" because setsockopt() wouldn't return an error if net.ipv6.bindv6only is true and optval (v6only in the example above) is false.)
> 
> I would volunteer to write a patch which introduces something like net.ipv6.bindv6only_enforced_silently if some maintainer would give me his ok.
> 
> If so, the question remains if
> 
> systemctl net.ipv6.bindv6only_enforced_silently = 1
> 
> should set systemctl.net.ipv6.bindv6only too or if an error should be returned if net.ipv6.bindv6only is false.

I am not convinced why you need this, and I am not in favor of
enfocing IPV6_V6ONLY, but... some points:

- We should allow system-admin to "enforce" IPV6_V6ONLY to 0 as well.
- CAP_NET_ADMIN users should always be able to use both modes
  (They can do sysctl anyway.)
- setsockopt should fail w/ EPERM if user tries to override.

--yoshfuji

RE: Disable IPv4-mapped - enforce IPV6_V6ONLY

[David Laight]

> > A proper solution would be to either return false if net.ipv6.bindv6only is true and optval is false
> (which would break downward compatibility because it wouldn't just be a default and setsockopt might
> return an error) or to introduce a new sysctl variable like net.ipv6.bindv6only_enforced_silently.
> ("silently" because setsockopt() wouldn't return an error if net.ipv6.bindv6only is true and optval
> (v6only in the example above) is false.)
> >
> > I would volunteer to write a patch which introduces something like
> net.ipv6.bindv6only_enforced_silently if some maintainer would give me his ok.
> >
> > If so, the question remains if
> >
> > systemctl net.ipv6.bindv6only_enforced_silently = 1
> >
> > should set systemctl.net.ipv6.bindv6only too or if an error should be returned if
> net.ipv6.bindv6only is false.
> 
> I am not convinced why you need this, and I am not in favor of
> enfocing IPV6_V6ONLY, but... some points:
> 
> - We should allow system-admin to "enforce" IPV6_V6ONLY to 0 as well.
> - CAP_NET_ADMIN users should always be able to use both modes
>   (They can do sysctl anyway.)
> - setsockopt should fail w/ EPERM if user tries to override.

I can imagine that some programs will always try to clear IPV6_V6ONLY
(maybe for portability with other OS which default to setting it
for security reasons) and will error-exit if it fails.
So non-silent enforcing could be a PITA.

OTOH there might be programs/systems where silent failure is wrong.

You really don't want to (globally) stop an application setting
IPV6_V6ONLY, such a program may well be creating separate IPv4
and IPv6 sockets.

Some of this needs to be part of some application wide 'security'
framework - that probably doesn't exist!

Should there also be similar controls for the use of IPv4
mapped addresses in actual on-the-wire IPv6 packets - eg those
destined for a remote gateway on an IPv6 only system?

	David

Re: Disable IPv4-mapped - enforce IPV6_V6ONLY

[Alexander Holler]

Am 25.02.2013 14:23, schrieb David Laight:
>>> A proper solution would be to either return false if net.ipv6.bindv6only is true and optval is false
>> (which would break downward compatibility because it wouldn't just be a default and setsockopt might
>> return an error) or to introduce a new sysctl variable like net.ipv6.bindv6only_enforced_silently.
>> ("silently" because setsockopt() wouldn't return an error if net.ipv6.bindv6only is true and optval
>> (v6only in the example above) is false.)
>>>
>>> I would volunteer to write a patch which introduces something like
>> net.ipv6.bindv6only_enforced_silently if some maintainer would give me his ok.
>>>
>>> If so, the question remains if
>>>
>>> systemctl net.ipv6.bindv6only_enforced_silently = 1
>>>
>>> should set systemctl.net.ipv6.bindv6only too or if an error should be returned if
>> net.ipv6.bindv6only is false.
>>
>> I am not convinced why you need this, and I am not in favor of
>> enfocing IPV6_V6ONLY, but... some points:

It's some kind of security feature I want to have. I just don't want to 
search for applications which are listening on IPv4 ports (too) even 
when only IPv6 was configured. There exists several of them.

>>
>> - We should allow system-admin to "enforce" IPV6_V6ONLY to 0 as well.
>> - CAP_NET_ADMIN users should always be able to use both modes
>>    (They can do sysctl anyway.)
>> - setsockopt should fail w/ EPERM if user tries to override.
>
> I can imagine that some programs will always try to clear IPV6_V6ONLY
> (maybe for portability with other OS which default to setting it
> for security reasons) and will error-exit if it fails.
> So non-silent enforcing could be a PITA.

Exactly.

> You really don't want to (globally) stop an application setting
> IPV6_V6ONLY, such a program may well be creating separate IPv4
> and IPv6 sockets.

Agreed. Applications which are setting IPV6_V6ONLY to true usually do 
know what they are doing. But some braindead (configured) applications 
are disabling it (and would bail out if setsockopt() would return an error).

>
> Some of this needs to be part of some application wide 'security'
> framework - that probably doesn't exist!
>
> Should there also be similar controls for the use of IPv4
> mapped addresses in actual on-the-wire IPv6 packets - eg those
> destined for a remote gateway on an IPv6 only system?

I think that can be handled by iptables by just blocking e.g. 
::ffff:0:0/96 and  ::0/96.

But it's a pain to find and take care of apps which are ignoring the 
default (net.ipv6.bindv6only) and are disabling IPV6_V6ONLY explicit for 
whatever reason.

Therefor I would like to have that 
net.ipv6.bindv6only_enforced_silently. Disabling IPv4 in general is not 
what I want.

Regards,

Alexander