F21 Self Contained Change: Remote Journal Logging

Zbigniew Jędrzejewski-Szmek zbyszek at in.waw.pl
Wed Apr 16 13:04:28 UTC 2014

On Tue, Apr 15, 2014 at 03:30:57PM -0400, Simo Sorce wrote:
> On Tue, 2014-04-15 at 20:28 +0200, Zbigniew Jędrzejewski-Szmek wrote:
> > On Tue, Apr 15, 2014 at 11:00:45AM -0400, Simo Sorce wrote:
> > > On Mon, 2014-04-14 at 15:07 +0200, Jaroslav Reznik wrote:
> > > > = Proposed Self Contained Change: Remote Journal Logging = 
> > > 
> > > > The communication between the two daemons is done over standard HTTPS, 
> > > > following rather simple rules, so it is possible to create alternate 
> > > > implementations without much work. For example, curl can be easily used to 
> > > > upload journal entries from a text file containing entries in the export 
> > > > format. Basically, the data are sent in an HTTP POST to /upload with Content-
> > > > Type: application/vnd.fdo.journal. When doing "live" forwarding, the size of 
> > > > the transfer cannot be known in advance, so Transfer-Encoding: chunked is 
> > > > used. All communication is encrypted, and the identity of both sides is 
> > > > verified by checking for appropriate signatures on the certificates.
> > 
> > > What are the pros of using HTTP if all you are doing are POSTS to a
> > > hardcoded URL ?
> > Using HTTP makes it possible to use e.g. use curl to upload some logs
> > from the commandline. It should also be fairly easy for people to write
> > e.g. Python code to upload logs. I also expect people to want to send
> > json formatted logs at some point, and the HTTP headers make things
> > fairly extensible. I think that using standard HTTP is easier than
> > designing a biderectional protocol.
> I understand  why HTTP looks convenient for some things, but really,
> aside for development, would you ever expect someone lo log to your
> interface except from a journald client ?
> > > HTTP seem like a bad idea in terms of security, certificates are
> > > notoriously very hard to manage, even with the help of things like
> > > certmonger, and hard to properly validate in most libraries today.
> > > 
> > > Let alone dealing with setting up a CA just for enabling remote logging
> > > (or otherwise painfully exchange fingerprints and white list
> > > certificates for each client-server pair.
> > >
> > > And please do not tell me this is deferred to the admin to figure out,
> > > because then it would mean this feature cannot seriously be used in
> > > normal setups.
> > I think you exaggarate a bit.
> I think you haven't tried for real :-)
> >  Managing certificates is annoying, true,
> > but there's lots of advice on the web and howto and various helper
> > software.
> There is a lot of "wrong" advice, mostly you find people telling other
> people to disable verification, and to use self signed certificates.
> >  I'd imagine that in a setup with a few servers one would create
> > the certificates on the receiver machine, copy&pasting some instructions
> > from Fedora docs, and scp them to the other hosts.
in current setup, I require (on both ends) for the certificate on the
other to be signed by a specified authority. So some of the questions
you ask don't really apply, since the certificates are supposed to be
generated specifically for this purpose.

> What I am asking is:
> How do you validate certificates on the client ?
I check if they are signed by a specified authoriy.

> Are you going to use white lists ?

> Are you going to depend on a CA white listed ?

> Are you going to create an extensions to be put in the certificates to
> restrict their use to logging ? Or are you going to allow to use any
> certificate as long as the CN matches the machine name ?
> Are you going to have white lists on the server ?
> Are you going to require client certificate authentication, or will you
> allow any anonymous client to flood your server with garbage ?
The client is authenticated by having a certificate signed by specified

> How do you generate certificates ?
> NSS comes with certutil, but it is not very flexible, I am not sure
> about wat GnuTLS comes with, but that library is not something I would
> like to depend on in the first place.
I leave the generation of the certificates to the admin. I personally used
openssl so far, but this shouldn't really matter.

> Also how are you going to harmonize client versus server management, the
> 2 stacks (NSS and GnuTLS) are quite different, having to learn not 1 but
> 2 stacks seem quite steep.
I don't think that's something that the user would care about. On
the programming side it's annoying though.

> > > Is there any reason why a better custom protocol that can be secured
> > > using things like SASL or GSSAPI is not used ?
> > It doesn't really fit well with the overall approach of using HTTP. But
> > I'm open to suggestions how to do this better. The Change page is so
> > obnoxiously detailed so that I can get feedback :)
> If you used something like protobuffers or dbus for the message
> formatting and use a socket for the transport where you can choose
> whether you want to do TLS vs GSSAPI easily (as you are not tied by the
> inability of HTTP to use anything but TLS) then you would have a much
> more flexible system. Also you wouldn't be tied to use 2 different
> crypto stacks in the same project which is really a shame. You have to
> duplicate everything and that will be prone to errors or
> incompatibilities and you'll have to use the lower common denominator if
> there are feature mismatches.
> You could also eventually tunnel over HTTPS, after it is just buffers
> going back and forth, but you wouldn't be tied to it.

I'll reconsider using SASL instead. I have the HTTPS-transport version
almost ready, so for now I'll go with that, to have a working
solution. There's still some other questions, mostly related to how
the data should be stored on the receiver, so I want to get it out for
people to test. The underlying transport is an implementation detail,
mostly visible in the way that authentication is done, so a new
transport can be added, and the old one deprecated or even removed.
Thank you for those suggestions.


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