Re: [Dnsmasq-discuss] Improve privacy by randomly selecting DNS server from a whitelist

[Sam Kuper]

On 10/10/2016, /dev/rob0  wrote:
> On Mon, Oct 10, 2016 at 02:53:44PM +0100, Sam Kuper wrote:
>> I was setting up an OpenWRT router recently, and wanted to be able
>> to improve the privacy of DNS requests made from that router and
>> from the PCs on the LAN.
>>
>> By handing off all the requests to *one* DNS provider, whether
>> that provider is the ISP, or Google, or someone else, privacy is
>> obviously compromised: that provider can very easily record *all*
>> the DNS requests sent via that router
>
> The ISP could, and they could do it regardless of the DNS forwarder
> chosen.  The ISP could even redirect all outbound queries to their
> own resolver, and through the magic of NAT, reply as the destination
> resolver.

Thanks for pointing this out!

Would DNSCrypt and/or DNSSEC protect against this? (I intend to learn
more about both in due course, but haven't got far enough with this
yet to be entirely confident in my estimation of the answer to that
question, sorry...)

>> (except, perhaps, in cases where the client is configured not
>> to seek a DNS forwarder on the LAN).
>
> Redirection covers this.  Just as with many hotels and hotspots,
> enter ANY IP address as your resolver, and it will "work", through
> the ISP's resolver.

Ditto.

> There are ways to "defeat" such an attack (where "defeat" means to
> detect it and to break your own ability to resolve names, so it's
> certainly not a clear victory.)  More on that below. [...]
>
>> Fortunately, there are numerous public DNS servers that I trust,
>> more or less, to return accurate results to DNS queries. I'll call
>> this the "semi-trusted set".
>>
>> Therefore, it occurred to me that a better option than simply
>> relying on *one* provider, would be to supply the router with a
>> list of IP addresses for the servers in the semi-trusted set, and
>> then, for each DNS query the router cannot answer from its own DNS
>> cache, have the router send the query to a randomly selected DNS
>> server from that list.
>
> This functionality does not exist in dnsmasq at this time.  But a
> Linux-specific way to do it would be to DNAT some of the queries
> using the "statistic" match.  See "iptables -m statistic -h" and the
> iptables-extensions(8) manual.

Cool suggestion. I wasn't aware of the "statistic" match options in
iptables. Will look into this more. On the face of it, it looks a bit
more fragile, and more prone to my making an error in setting it up,
than having a suitable capability present in Dnsmasq would be; but as
the latter doesn't presently exist, iptables may well be my best bet
:)

>> That way, the clients would (I hope) receive trustworthy replies,
>> and none of the providers would be able to record more than a
>> random subset of the requests. This might come at the cost of
>> slightly slower average response times for DNS queries, but for my
>> use case, this would be perfectly acceptable.
>>
>> While searching for a way to do this, I learned that Dnsmasq is
>> included by default in OpenWRT. Learning, in turn, about Dnsmasq,
>> made me optimistic that it might be possible to configure or extend
>> Dnsmasq to achieve the desired functionality described above.
>>
>> I would be grateful to know:
>>
>> - whether, and if so, why, the desiderata I described are a Bad
>> Idea. (I hope not, but it's always good to have a sanity check.)
>
> It doesn't seem important to me, but I am a "full control" control
> freak who runs his own recursive resolver.  And that's how I defeat
> the redirection attacks.
>
> See, a recursive resolver makes queries directly to the various
> authoritative NS hosts.  Those queries do not have the "RD" bit
> (recursion desired) set, and the resolver will only accept replies
> which have the "AA" bit (authoritative) set.
>
> Replies from a recursive resolver do not have AA, so when my ISP gets
> that hare-brained idea again, to redirect queries to their broken
> resolver, immediately, I know.  (Because nothing resolves.)

Thanks for this, too. I was hoping for a solution that was more
lightweight than running my own recursive resolver, but it's an option
I will definitely consider.

> DNSSEC validation also helps here.  The root and most top-level zones
> are signed, and if those signatures are missing or broken, again, I
> will see that nothing resolves.

Understood.

>> - whether anyone on this list knows of a way to achieve the desired
>> functionality by configuring existing software available within
>> OpenWRT, and if so, how. (Maybe there's a package, or a setting,
>> that does exactly what I'm after, and I've just never heard of it.)
>> Please reply to me off-list if the answer is not relevant to
>> Dnsmasq.
>
> The iptables statistic match is probably not in stock openwrt, so
> that must be installed.

I think you are correct. On a stock OpenWRT CLI:

# iptables -h | grep -i statistic | wc -l
0

> What I do, and have posted before on this list about, is to run
> dnsmasq for DHCP and local 

Re: [Dnsmasq-discuss] Improve privacy by randomly selecting DNS server from a whitelist

[/dev/rob0]

On Mon, Oct 10, 2016 at 02:53:44PM +0100, Sam Kuper wrote:
> I was setting up an OpenWRT router recently, and wanted to be able 
> to improve the privacy of DNS requests made from that router and 
> from the PCs on the LAN.
> 
> By handing off all the requests to *one* DNS provider, whether
> that provider is the ISP, or Google, or someone else, privacy is 
> obviously compromised: that provider can very easily record *all* 
> the DNS requests sent via that router

The ISP could, and they could do it regardless of the DNS forwarder 
chosen.  The ISP could even redirect all outbound queries to their 
own resolver, and through the magic of NAT, reply as the destination 
resolver.

Furthermore the ISP has access to the personal information of the 
account holder.  They have the ability to make an association of IP 
address to customer.

I doubt it's so easy for Google to get personally identifying 
information from Google Public DNS.  I suspect that data is of 
interest to them in determining site rankings, mostly.  A side 
benefit is to see the DNS attacks which are underway.  I suspect 
Google has multiple full-time analysts looking at those attacks.
(Perhaps I should say, I *hope* they do.)

> (except, perhaps, in cases where the client is configured to no
> to seek a DNS forwarder on the LAN).

Redirection covers this.  Just as with many hotels and hotspots, 
enter ANY IP address as your resolver, and it will "work", through 
the ISP's resolver.

There are ways to "defeat" such an attack (where "defeat" means to 
detect it and to break your own ability to resolve names, so it's 
certainly not a clear victory.)  More on that below.

> Unfortunately, there are no public DNS providers who I trust not to
> record this sort of information for longer than necessary, nor any
> whom I trust never to abuse that sort of information. (Perhaps you
> think my feelings about this are wrong, but please bear with me.)

Again I'd definitely be more concerned about the ISP than about el 
Goog.  I'm not speaking as a Google fanboy (I'm not one!), just 
considering the technical issues.  (For one thing, note that a DNS 
query cannot identify why you were querying; perhaps it wasn't even 
for HTTP.)

But, that's how it is for most of us: we have to deal with an ISP if 
we want to get online.

> Fortunately, there are numerous public DNS servers that I trust, 
> more or less, to return accurate results to DNS queries. I'll call 
> this the "semi-trusted set".
> 
> Therefore, it occurred to me that a better option than simply 
> relying on *one* provider, would be to supply the router with a 
> list of IP addresses for the servers in the semi-trusted set, and 
> then, for each DNS query the router cannot answer from its own DNS 
> cache, have the router send the query to a randomly selected DNS 
> server from that list.

This functionality does not exist in dnsmasq at this time.  But a 
Linux-specific way to do it would be to DNAT some of the queries 
using the "statistic" match.  See "iptables -m statistic -h" and the 
iptables-extensions(8) manual.

> That way, the clients would (I hope) receive trustworthy replies, 
> and none of the providers would be able to record more than a 
> random subset of the requests. This might come at the cost of 
> slightly slower average response times for DNS queries, but for my 
> use case, this would be perfectly acceptable.
> 
> While searching for a way to do this, I learned that Dnsmasq is 
> included by default in OpenWRT. Learning, in turn, about Dnsmasq, 
> made me optimistic that it might be possible to configure or extend 
> Dnsmasq to achieve the desired functionality described above.
> 
> I would be grateful to know:
> 
> - whether, and if so, why, the desiderata I described are a Bad 
> Idea. (I hope not, but it's always good to have a sanity check.)

It doesn't seem important to me, but I am a "full control" control 
freak who runs his own recursive resolver.  And that's how I defeat 
the redirection attacks.

See, a recursive resolver makes queries directly to the various 
authoritative NS hosts.  Those queries do not have the "RD" bit 
(recursion desired) set, and the resolver will only accept replies 
which have the "AA" bit (authoritative) set.

Replies from a recursive resolver do not have AA, so when my ISP gets 
that hare-brained idea again, to redirect queries to their broken 
resolver, immediately, I know.  (Because nothing resolves.)

DNSSEC validation also helps here.  The root and most top-level zones 
are signed, and if those signatures are missing or broken, again, I 
will see that nothing resolves.

> - whether anyone on this list knows of a way to achieve the desired 
> functionality by configuring existing software available within 
> OpenWRT, and if so, how. (Maybe there's a package, or a setting, 
> that does exactly what I'm after, and I've just never heard of it.) 
> Please reply to me off-list if the answer is not relevant to 
> Dnsmasq.

The iptables 

Re: [Dnsmasq-discuss] Improve privacy by randomly selecting DNS server from a whitelist

[Sam Kuper]

On 10/10/2016, Sam Kuper  wrote:
> Dear Dnsmasq folk [...]

Apologies, some of the formatting went awry in my previous message.
Let me try that again.


Dear Dnsmasq folk,

This is my first foray onto the mailing list, and I am not very
experienced with Dnsmasq or indeed DNS, so please be gentle.

I was setting up an OpenWRT router recently, and wanted to be able to
improve the privacy of DNS requests made from that router and from the
PCs on the LAN.

By handing off all the requests to *one* DNS provider, whether that
provider is the ISP, or Google, or someone else, privacy is obviously
compromised: that provider can very easily record *all* the DNS
requests sent via that router (except, perhaps, in cases where the
client is configured to not to seek a DNS forwarder on the LAN).

Unfortunately, there are no public DNS providers who I trust not to
record this sort of information for longer than necessary, nor any
whom I trust never to abuse that sort of information. (Perhaps you
think my feelings about this are wrong, but please bear with me.)

Fortunately, there are numerous public DNS servers that I trust, more
or less, to return accurate results to DNS queries. I'll call this the
"semi-trusted set".

Therefore, it occurred to me that a better option than simply relying
on *one* provider, would be to supply the router with a list of IP
addresses for the servers in the semi-trusted set, and then, for each
DNS query the router cannot answer from its own DNS cache, have the
router send the query to a randomly selected DNS server from that
list. That way, the clients would (I hope) receive trustworthy
replies, and none of the providers would be able to record more than a
random subset of the requests. This might come at the cost of slightly
slower average response times for DNS queries, but for my use case,
this would be perfectly acceptable.

While searching for a way to do this, I learned that Dnsmasq is
included by default in OpenWRT. Learning, in turn, about Dnsmasq, made
me optimistic that it might be possible to configure or extend Dnsmasq
to achieve the desired functionality described above.

I would be grateful to know:

- whether, and if so, why, the desiderata I described are a Bad Idea.
(I hope not, but it's always good to have a sanity check.)

- whether anyone on this list knows of a way to achieve the desired
functionality by configuring existing software available within
OpenWRT, and if so, how. (Maybe there's a package, or a setting, that
does exactly what I'm after, and I've just never heard of it.) Please
reply to me off-list if the answer is not relevant to Dnsmasq.

- whether, if the desired functionality is not currently readily
available within OpenWRT, but could be made available by extending
Dnsmasq, any of you on the list would be keen to implement that
functionality (Simon Kelley, maybe?), or to donate funds towards such
an effort.

Many thanks.

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[Dnsmasq-discuss] Improve privacy by randomly selecting DNS server from a whitelist

[Sam Kuper]

Dear Dnsmasq folk,

This is my first foray onto the mailing list, and I am not very
experienced with Dnsmasq or indeed DNS, so please be gentle.

I was setting up an OpenWRT router recently, and wanted to be able to
improve the privacy of DNS requests made from that router and from the
PCs on the LAN.

By handing off all the requests to *one* DNS provider, whether that
provider is the ISP, or Google, or someone else, privacy is obviously
compromised: that provider can very easily record *all* the DNS
requests sent via that router (except, perhaps, in cases where the
client is configured to not to seek a DNS forwarder on the LAN).

Unfortunately, there are no public DNS providers who I trust not to
record this sort of information for longer than necessary, nor any
whom I trust never to abuse that sort of information. (Perhaps you
think my feelings about this are wrong, but please bear with me.)

Fortunately, there are numerous public DNS servers that I trust, more
or less, to return accurate results to DNS queries. I'll call this the
"semi-trusted set".

Therefore, it occurred to me that a better option than simply relying
on *one* provider, would be to supply the router with a list of IP
addresses for the servers in the semi-trusted set, and then, for each
DNS query the router cannot answer from its own DNS cache, have the
router send the query to a randomly selected DNS server from that
list. That way, the clients would (I hope) receive trustworthy
replies, and none of the providers would be able to record more than a
random subset of the requests. This might come at the cost of slightly
slower average response times for DNS queries, but for my use case,
this would be perfectly acceptable.

While searching for a way to do this, I learned that Dnsmasq is
included by default in OpenWRT. Learning, in turn, about Dnsmasq, made
me optimistic that it might be possible to configure or extend Dnsmasq
to achieve the desired functionality described above.

I would be grateful to know:

whether, and if so, why, the desiderata I described are a Bad Idea. (I
hope not, but it's always good to have a sanity check.)
whether anyone on this list knows of a way to achieve the desired
functionality by configuring existing software available within
OpenWRT, and if so, how. (Maybe there's a package, or a setting, that
does exactly what I'm after, and I've just never heard of it.) Please
reply to me off-list if the answer is not relevant to Dnsmasq.
whether, if the desired functionality is not currently readily
available within OpenWRT, but could be made available by extending
Dnsmasq, any of you on the list would be keen to implement that
functionality (Simon Kelley, maybe?), or to donate funds towards such
an effort.

Many thanks.

___
Dnsmasq-discuss mailing list
Dnsmasq-discuss@lists.thekelleys.org.uk
http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss