why was DNS/ICMP removed from Qubes manager/firewall in R4?

[simon....@gmail.com]

In 3, if i clicked on "block connections" in the Qubes manager firewall section, there was (if memory serves me) an option to block DNS and ICMP.

That is not present in R4 (though docs say you can disable DNS and ICMP manually)

I'm just wondering what the logic behind the removal was? I would have thought that a general user who clicks "block connections" on Qube would not expect the qube to be able to actually send out and receive network packets such as DNS or ICMP. This presents information leakage scenarios (default DNS lookups of given qube) and also potential egress vectors if a qube is ever compromised (DNS tunnelling, ICMP tunnelling).

TIA

[Marek Marczykowski-Górecki]

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Let me quote full text you can find on firewall tab there:

NOTE: To block all network access, set Networking to (none) on the
Basic settings tab. This tab provides a very simplified firewall
configuration. All DNS requests and ICMP (pings) will be allowed. For
more granular control, use the command line tool qvm-firewall.

There is clear message what to do if you want to cut the qube from the
network.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
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[simon....@gmail.com]

As I said, I understand the documentation is correct. thats not my question. My question is why was it removed as an option when the firewall box itself in network manager says "Deny network access except..."

My point is it is counter intuitive. If it says "deny network access exccept..." then there is an expectation that it will deny network access except for what is specified. There used to be tick buttons (allow updates/allow ICMP/allow DNS), which made it clear on the granular control there - but were removed in R4. The underlying subsytems you can still do that, sure.

Can I suggest that the wording "deny network access except..." is changed to "Deny TCP and UDP access except ..." for the avoidance of any doubt.

[simon....@gmail.com]

https://github.com/QubesOS/qubes-manager/pull/153

[ashleyb...@tutanota.com]

There is an issue that talks about the change: https://github.com/QubesOS/qubes-issues/issues/4141

They are willing to port it back to how it should be if someone does the interface to re-add those options.

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Feb 14, 2019, 11:59 AM by simon....@gmail.com:

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[ashleyb...@tutanota.com]

Hopefully one day they revert it back to how it was in 3.2. A very common use-case for the firewall is likely to ensure things like DNS requests do not happen through the normal means (and instead go over something like Tor or a VPN). Unfortunately, the current config does not make it very obvious that someone should block DNS ports. Making it very easy for someone to shoot themselves in the foot because the interface is not intuitive (it says it blocks all traffic other than what is specified and then later modifies this saying "just kidding, we let DNS through")

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Feb 14, 2019, 11:59 AM by simon....@gmail.com:

On Thursday, February 14, 2019 at 11:54:28 AM UTC, simon....@gmail.com wrote:

[unman]

On Thu, Feb 14, 2019 at 03:13:50PM +0100, ashleyb...@tutanota.com wrote:
> Hopefully one day they revert it back to how it was in 3.2. A very common use-case for the firewall is likely to ensure things like DNS requests do not happen through the normal means (and instead go over something like Tor or a VPN). Unfortunately, the current config does not make it very obvious that someone should block DNS ports. Making it very easy for someone to shoot themselves in the foot because the interface is not intuitive (it says it blocks all traffic other than what is specified and then later modifies this saying "just kidding, we let DNS through")
>

> Feb 14, 2019, 11:59 AM by simon....@gmail.com:
>
> > On Thursday, February 14, 2019 at 11:54:28 AM UTC, simon....@gmail.com wrote:
> >
> >> > On Wed, Feb 13, 2019 at 08:42:10AM -0800, >> simon....@gmail.com <mailto:simon....@gmail.com>>> wrote:
> >> > > In 3, if i clicked on "block connections" in the Qubes manager firewall section, there was (if memory serves me) an option to block DNS and ICMP.
> >> > >
> >> > > That is not present in R4 (though docs say you can disable DNS and ICMP manually)
> >> > >
> >> > > I'm just wondering what the logic behind the removal was? I would have thought that a general user who clicks "block connections" on Qube would not expect the qube to be able to actually send out and receive network packets such as DNS or ICMP. This presents information leakage scenarios (default DNS lookups of given qube) and also potential egress vectors if a qube is ever compromised (DNS tunnelling, ICMP tunnelling).
> >> >

> >> As I said, I understand the documentation is correct. thats not my question. My question is why was it removed as an option when the firewall box itself in network manager says "Deny network access except..."
> >>
> >> My point is it is counter intuitive. If it says "deny network access exccept..." then there is an expectation that it will deny network access except for what is specified. There used to be tick buttons (allow updates/allow ICMP/allow DNS), which made it clear on the granular control there - but were removed in R4. The underlying subsytems you can still do that, sure.
> >>
> >> Can I suggest that the wording "deny network access except..." is changed to "Deny TCP and UDP access except ..." for the avoidance of any doubt.
> >>
> >
> >

> > https://github.com/QubesOS/qubes-manager/pull/153 <https://github.com/QubesOS/qubes-manager/pull/153>
> >

Please dont top post - it breaks the thread of the conversation.

I dont find the current position confusing, since the DNS and ICMP
position is clearly stated in the NOTE at the bottom of the window.

Simon, to answer your original question, there are many features in 4.0
which are aimed at simplifying use of Qubes. I think this is one of
them.
The underlying issue is this: if you want to set a firewall rule using a
named site, then you must not only set the rule, (and the resolution
will be set at the upstream firewall), but you must also enable DNS -
otherwise your qube will not be able to resolve the address, even
though you have correctly set the firewall rule.
This adds a layer of complexity which a naive user would not understand.

The decision was made to keep DNS open in a trade off between usability
and security.
There's also an underlying assumption that users who want more will be
able to negotiate command line tools. This assumption may be misplaced.
There are many users (not only of Qubes) who consider themselves "power
users" (never understood what that meant), but dont seem able to
understand iptables or use anything except a GUI. (Just to be clear, I'm
not aiming at any contributor here.)

As for ICMP, it's a moot point whether you should ever block ICMP at
firewall level. Again, the benefit of having ICMP enabled is that basic
network mechanisms are enabled, and basic diagnostic tools are
available. It's a trade off between security and usability.

As with *all* parts of Qubes, if you dont like the defaults change them
on your system.
If you like, propose a change by submitting a PR.
There's an open issue on exactly this, where Marta outlined the issue and
invited contributions that would allow the change and also keep clarity
for naive users (my gloss). No one has yet stepped up.

unman

[simon....@gmail.com]

Thanks Unman, thats a detailed and logical explanation as to where its gone. It makes a bit more sense now. As I said, it wasn't anything to do with documentation, more around managing a users expectations. If I have some time I will try to get involved in making some changes to the manager firewall section, but that will not likely be for a few months due to commitments.

Thanks again