Re: DOS by unprivileged user

[Miguel Ojeda]

On Mon, Apr 30, 2018 at 12:00 PM, Ferry Toth <ftoth@xxxxxxxxxx> wrote:
> Op woensdag 25 april 2018 16:54:59 CEST schreef Alan Cox:
>> > > I think memory allocation and io waits can't be decoupled from
>> > > scheduling as they are now.
>> >
>> > The scheduler is not decoupled from either, it is intimately involved
>> > in both.  However, none of the decision making smarts for either reside
>> > in the scheduler, nor should they.
>>
>> It belongs in both.
>>
>> Classical Unix systems never had this problem because they respond to
>> thrashing by ensuring that all processes consumed CPU and made some
>> progress. Linux handles it by thrashing itself to dealth while BSD always
>> handled it by moving from paging more towards swapping and behaving like
>> a swap bound batch machine.
>>
>> Linux thrashes itself to death, the classic BSD algorithn instead throws
>> fairness out of the window under extreme load to prevent it. It might take
>> a few seconds but at least you will get your prompt back.
>>
>> Alan
>>
> I haven t tried BSD.
>
> But when I was young I allocated 10MB on a HP9000 (UX) with 1MB of RAM. People wanted to launch me out of the window (18th floor).
>
> I did not want to say Unix was better, only with so much emphasis on security I' m surprised how easy it is for a regular user to bring linux to on it s knees.

While it is true that things can be improved/tweaked for typical
desktop/single user usage; this isn't really a security issue. For
shared systems, there are a few ways to soft/hard limit resources:
nice, *limit, cgroups, systemd limits, containers/VMs...

Cheers,
Miguel