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Howto prevent fork bombing

Posted on 2005-03-18
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Last Modified: 2008-03-10
Hi all

I just read this article [1] about linux boxes that  (with exception of a few)  they are  vulnerable by default to fork bombing.

Can anybody help me to configure my machines to prevent faulty programs and malicous users to bring down the box with something as simple as fork bombs.


With kind regards


Ramses (x_terminat_or_3)
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Question by:x_terminat_or_3
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by:x_terminat_or_3
ID: 13580930
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wesly_chen earned 2000 total points
ID: 13581013
Hi,

    It's good to know about the security issue about Linux.

    It seems that you need to check "ulimit" and make sure there is no "unlimit" for process. And then put it in /etc/profile
or /etc/cshrc (or /etc/.login) to prevent this problem.

   However, it depends on the application or how powerful your Linux server is. Some Web server or database
software need the higher process limit to run without problem. Just be careful when you set ulimit.

Regards,

Wesly
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by:x_terminat_or_3
ID: 13581040
I see here that an unpriviledged account has the ulimit's max processes set to 8192

What kind of user needs 8192 concurent processes running?

It isn't mentioned in the man pages, but does the restriction set by ulimit to ALL users, or does it have to be set on a per-user base?


Kind regards


Ramses


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Expert Comment

by:wesly_chen
ID: 13581050
Hi,

   Set in /etc/profile, /etc/cshrc and (/etc/.login ? not with Linux at this moment) so every user login will
be set. Option (-h) will be "hard" limit so user can not use "ulimit" to reset it.

Wesly
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by:x_terminat_or_3
ID: 13581527
This is the current setting I found in /etc/profile

ulimit -S -c 0 > /dev/null 2>&1


This produces the following max:


core file size            (blocks, -c) 0
data seg size            (kbytes, -d) unlimited
file size            (blocks, -f) unlimited
pending signals                  (-i) 1024
max locked memory      (kbytes, -l) 32
max memory size            (kbytes, -m) unlimited
open files                  (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues      (bytes, -q) 819200
stack size            (kbytes, -s) 8192
cpu time            (seconds, -t) unlimited
max user processes            (-u) 8180
virtual memory            (kbytes, -v) unlimited
file locks                  (-x) unlimited

I want to set some reasonable defaults.  Has anybody run into users that require to have more then a few hundered concurent processes running? (as oposed to 8192)

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by:x_terminat_or_3
ID: 13582267
Ok that latst question was more retorical...



Works for me  Thanks!
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