linux-kernel - Re: DOS by unprivileged user

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Message-ID: <CANiq72kkGrn0fGVMB=ht48_wM4Fy=KotiHed+efB2Gf9heeM6Q@mail.gmail.com>
Date:   Mon, 30 Apr 2018 12:35:25 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Ferry Toth <ftoth@...fort.nl>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Mike Galbraith <efault@....de>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: DOS by unprivileged user

On Mon, Apr 30, 2018 at 12:00 PM, Ferry Toth <ftoth@...fort.nl> 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