Re: Priority Increasing

From: Mike Silbersack (silby_at_silby.com)
Date: 02/28/05

  • Next message: Roland Dowdeswell: "Re: RFC: backporting GEOM to the 4.x branch" 
    Date: Mon, 28 Feb 2005 03:30:01 -0600 (CST)
To: Ashwin Chandra <ashcs@ucla.edu>

    On Sun, 27 Feb 2005, Ashwin Chandra wrote:

    > Hi all, Ive been trying to counter the malicious effects of a forkbomb
    > by setting the forkbomb parent and children to a PRI_MAX priority,
    > although this is not having any effect on the system load.
    >
    > Basically in my code when I know which process is acting maliciously
    > (forkbomb), I run the following simple code:

    If you're sure that the program is a forkbomb, why not modify the forkbomb
    protection that is already present in kern_fork.c:

    tsleep(&forksleep, PUSER, "fork", hz / 2);

    What it does at present is whenever you try to fork and you've hit your
    process limit (see limits(1)), it puts your process to sleep for .5
    seconds. If you have a better way to tell if something is a forkbomb, why
    not just do the same thing, perhaps with a shorter sleep.

    Don't try too hard to defeat forkbombs, though. Whenever it's been
    discussed, someone has invariably pointed out that you could just fork 750
    processes, and then have those 750 do something else which is kernel
    intensive, like reading/writing 1 byte at a time.

    In other words, limiting the maximum number of processes a user can have
    must be part of the equation - and we probably set that limit too high by
    default. :)

    Mike "Silby" Silbersack
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  • Next message: Roland Dowdeswell: "Re: RFC: backporting GEOM to the 4.x branch"

    Relevant Pages

    • Fw: Priority Increasing
      ... The forkbomb program I wrote is just one parent that forks 750 or so ... The children do not fork. ... I see the overhead of forking could ... I suggest you fix the program so that it doesn't ...
      (freebsd-hackers)
    • Re: Fw: Priority Increasing
      ... > The forkbomb program I wrote is just one parent that forks 750 or so ... The children do not fork. ... You are talking about malloc'ing almost 30GB of memory and having 750 ...
      (freebsd-hackers)