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Re: [RFC] apt-zeroconf 0.1



On Mon, 2006-11-20 at 10:16 +0100, Andreas Barth wrote: 
> * Franz Pletz (fpletz@franz-pletz.org) [061119 21:06]:
> > On Sun, Nov 19, 2006 at 07:07:03PM +0100, Reinhard Tartler wrote:
> > > Why don't you install a line like
> > > 
> > > >    e.g. deb http://127.0.0.1:1618/debian main contrib non-free
> > > 
> > > in /etc/apt/sources.list.d, and be done with it? That's what I'd
> > > call
> > > zero config.
> > > 
> > > You would have to convince apt to prefer apt-zeroconfig sources 
> > > over
> > > 'regular' HTTP sources, so that it only uses the slow line when
the
> > > package couldn't be found in the neighbourhood. I believe this
could be
> > > tweaked be tuning /etc/apt/preferences. If not, you would have to
hack
> > > up apt a bit.
> > 
> > We also pondered with that idea, but with this configuration
modifying
> > apt is definitely required. Apt associates a server to every package
> > and version where to get the debs from. We are not building package
> > lists from all hosts in the network because this would compromise
the
> > security of the whole network.
> 
> Two questions:
> 
> 1. Why don't you add the appropriate proxy-line to to apt via
apt.conf.d
> (e.g. as conffile, so you don't have to care about that later on)?

This is basically what our proxy mode supports, but we haven't yet
automated the process of adding apt-zeroconf to apt. We should probably
do that, right. We are thinking  about using debconf for this to let
users a choice how may like to use azc only for some of there apt
sources.

> 2. What security threats do you see?

Since there is a lot of work done on apt security most cases are handled
right through apt itself. But we maybe should azc let do some checks:
  Imagine there is someone in the network who offers corrupted files and
you download through azc. apt will not install them because of
missmatching hashes (as long nobody is able to crack md5, sha at once -
but this is not a azc specific problem). So you fail to install the
stuff you wanted and the you don't know why - and especially not who
is to blame. If you try to install the package again you will fail again
as log as there is only on person who offers the file.

As long as we don't check the package within azc its not possible to
react automatic to an corrupted file since azc doesn't recognizes that
apt fails to install a file. But this would be good - for example for
ignoring the node at further file searches to avoid to download the same
corrupted file again.

This would add some load to azc since the checking cost cpu and hd time
so it should be optional but turned on by default. I hope in the next
release there will be a proper logging system. With that you can figure
out who offered the corrupted file by grep'ing the log files.

Not official reps are always a security risk... especially those that
contain...
* Packages without hashes
* Pkgs without sign
* PkgLists without sign

For now we don't handle package lists (and/or pdiffs) with azc - they
are always fetched from the fallback-server - but may add it this to azc
in future. Since pkg lists are also signed it shouldn't be a security
hole. At all its much more complicated to cache the pkg lists so this
will be done one day in future - perhaps.

Florian Ludwig

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