Messages in this thread | | | Date | Tue, 08 Mar 2005 17:28:56 +1100 | From | Peter Williams <> | Subject | Re: [PATCH] [request for inclusion] Realtime LSM |
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Ingo Molnar wrote: > * Peter Williams <pwil3058@bigpond.net.au> wrote: > > >>I don't object to rlimits per se and I think that they are useful but >>not as a sole solution to this problem. Being able to give a task >>preferential treatment is a permissions issue and should be solved as >>one. >> >>Having RT cpu usage limits on tasks is a useful tool to have when >>granting normal users the privilege of running tasks as RT tasks so >>that you can limit the damage that they can do BUT the presence of a >>limit on a task is not a very good criterion for granting that >>privilege. > > > i think you are talking about my rlimit patch (the 'RT CPU limit' patch) > - but that one is not in discussion here. > > what is being discussed currently is the other rlimit patch (from Chris > Wright and Matt Mackall) which implements a simple rlimit ceiling for > the RT (and nice) priorities a task can set. The rlimit defaults to 0, > meaning no change in behavior by default. A value of 50 means RT > priority levels 1-50 are allowed. A value of 100 means all 99 privilege > levels from 1 to 99 are allowed. CAP_SYS_NICE is blanket permission. > It's all pretty finegrained and and it's a quite straightforward > extension of what we have today.
OK. My misunderstanding.
But the patch you describe still seems a little loose to me in that it doesn't control both which users AND which programs they can run. Although I suppose that can be managed by suitable setting of file permissions?
Also I presume that root privileges are needed to set the rlimits which means that the program has to be setuid root or run from a setuid root wrapper. In the first of these cases the program will be running for a (hopefully) short while with way more privilege than it needs. This is why I'm attracted to mechanisms that allow programs to be given a subset of root's privileges and only for specified users.
I would be nice to have a solution to this particular problem that fits in with such a generalized "granular" privilege mechanism (when/if such a mechanism becomes available in the future) rather than a quirky fix that is specific to this problem and doesn't generalize well to similar problems when they arise in the future. However, I agree with your opinion that granting CAP_SYS_NICE is dangerous without some limit on the priority levels is dangerous and think that a generalized "granular" privilege mechanism would need to include such restrictions.
> The patch does not attempt to do any > "damage control" of abuse caused by RT tasks, and is hence much simpler > than my patch or Con's SCHED_ISO patch. ("damage control" could be done > from userspace anyway)
Yes. In kernel "damage control" is an optional extra not a necessity with this solution. Not so sure about with the RT LSB solution though.
Peter -- Peter Williams pwil3058@bigpond.net.au
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