Re: XSA-180 follow-up: repurpose xenconsoled for logging

[Wei Liu <wei.liu2@citrix.com>]

On Mon, Jun 06, 2016 at 03:47:37PM -0500, Doug Goldstein wrote:
> On 6/6/16 5:12 AM, George Dunlap wrote:
> > On 03/06/16 18:38, Andrew Cooper wrote:
> >> On 01/06/16 15:00, Wei Liu wrote:
> >>> Hi all
> >>>
> 
> <snip>
> 
> > FWIW, the libvirt project has exactly the same problem, and they did the
> > analog of what Wei is proposing -- they added a new daemon, virtlogd, to
> > handle all the console and debug log rotation in a fashion resistant to
> > DoSing.  Without reading their discussion, it's reasonable to assume
> > that using system logging was at least considered using system-level
> > logging before deciding to write their own code.
> 
> If I recall they use RPCs and the logs are generated as a best effort to
> not block QEMU.
> 

Does that mean it's more or less equivalent to O_NONBLOCK?

Is that configurable?  We might actually want to block in some cases.

> > 
> > We already have a daemon to do logging of consoles; it just doesn't have
> > any of the logrotate features that are needed to make it robust against
> > DoS.  There's no sense in having log rotation code in two places, so
> > upgrading xenconsoled to do what virtlogd is doing makes more sense than
> > say, either writing our own, or stealing virtlogd.
> 
> What if we made xl / libxl really good at the limited scope of things it
> should be good at and left the other bits to others. At this point it
> seems like yet another feature that xl / libxl is gaining that matches
> what libvirt does. Maybe an approach is something you appear to suggest
> and just point people to virtlogd and ask the libvirt guys if they would
> make it a separate package. Honestly it seems like xl could slim down
> from a feature set perspective and focus on improving libxl / libvirt
> interaction. That's something that the Xen community has been interested
> in to better support OpenStack anyway.
> 

To clarify: xenconsoled is not part of xl / libxl. I think it you're
talking about xen toolstack in general.

I think we can ask libvirt maintainers: 1. if it is possible to make
virtlogd a separate package, 2. if they can maintain a stable interface.

Then we can think about how to make sensible suggestions and provide a
way for sysamdins to configure that.

No matter what solution we end up with, the work to integrate that with
xl / libxl is unavoidable.

Wei.

> Just my 2 cents.
> 
> -- 
> Doug Goldstein
> 




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