Critical Denial of Service bugs in Discover

[Harald Sitter]

On Thu, Feb 10, 2022 at 1:11 PM Aleix Pol <aleixpol at kde.org> wrote:
>
> On Thu, Feb 10, 2022 at 11:05 AM Ben Cooksley <bcooksley at kde.org> wrote:
> >
> >
> >
> > On Thu, Feb 10, 2022 at 8:20 AM Aleix Pol <aleixpol at kde.org> wrote:
> >>
> >> [Snip]
> >>
> >> We still haven't discussed here is how to prevent this problem from
> >> happening again.
> >>
> >> If we don't have information about what is happening, we cannot fix problems.
> >
> >
> > Part of the issue here is that the problem only came to Sysadmin attention very recently, when the system ran out of disk space as a result of growing log files.
> > It was at that point we realised we had a serious problem.
> >
> > Prior to that the system load hadn't climbed to dangerous levels (> number of CPU cores) and Apache was keeping up with the traffic, so none of our other monitoring was tripped.
> >
> > If you have any thoughts on what sort of information you are thinking of that would be helpful.
>
> We could have plots of the amount of queries we get with a KNewStuff/*
> user-agent over time and their distribution.
>
> > It would definitely be helpful though to know when new software is going to be released that will be interacting with the servers as we will then be able to monitor for abnormalities.
>
> We make big announcements of every Plasma release... (?)
>
> >> Is there anything that could be done in this front? The issue here
> >> could have been addressed months ago, we just never knew it was
> >> happening.
> >
> >
> > One possibility that did occur to me today would be for us to integrate some kind of killswitch that our applications would check on first initialisation of functionality that talks to KDE.org servers.
> > This would allow us to disable the functionality in question on user systems.
> >
> > The check would only be done on first initialization to keep load low, while still ensuring all users eventually are affected by the killswitch (as they will eventually need to logout/reboot for some reason or another).
> >
> > The killswitch would probably work best if it had some kind of version check in it so we could specify which versions are disabled.
> > That would allow for subsequent updates - once delivered by distributions - to restore the functionality (while leaving it disabled for those who haven't updated).
>
> The file we are serving here effectively is the kill switch to all of KNewStuff.

I'm a bit late to the party but for future reference I think this
was/is an architectural scaling problem on the server side as much as
a bug on the client. If just https load is the problem then the
"hotfix" is to use a HTTP load balancer until fixes make it into the
clients, killing the clients is like the last resort ever. I'm sure we
have the money to afford a bunch of cloud nodes serving as selective
proxy caches for a month to balance out the KNS load on the canonical
server.

HS