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--- notas:seguridad:understanding_bash_fork_bomb [2014/06/03 14:05] – creado cayu
+++ notas:seguridad:understanding_bash_fork_bomb [Fecha desconocida] (actual) – borrado - editor externo (Fecha desconocida) 127.0.0.1
@@ Línea 1: / Línea 1: @@
-===== Understanding Bash fork() bomb ~ :(){ :|:& };: =====
-**Q.** Can you explain following bash code or bash fork() bomb?
-:(){ :|:& };:
-**A.** This is a bash function. It gets called recursively (recursive function). This is most horrible code for any Unix / Linux box. It is often used by sys admin to test user processes limitations (Linux process limits can be configured via /etc/security/limits.conf and PAM).
-Once a successful fork bomb has been activated in a system it may not be possible to resume normal operation without rebooting, as the only solution to a fork bomb is to destroy all instances of it.
-[Warning examples may crash your computer] WARNING! These examples may crash your computer if executed.
-Understanding :(){ :|:& };: fork() bomb code
-:() - It is a function name. It accepts no arguments at all. Generally, bash function is defined as follows:
-<code bash>
-foo(){
- arg1=$1
- echo ''
- #do_something on $arg argument
-}
-</code>
-fork() bomb is defined as follows:
-<code bash>
-:(){
- :|:&
-};:
-</code>
-**
-:|:** - Next it call itself using programming technique called recursion and pipes the output to another call of the function ':'. The worst part is function get called two times to bomb your system.
-**&** - Puts the function call in the background so child cannot die at all and start eating system resources.
-**;** - Terminate the function definition
-**:** - Call (run) the function aka set the fork() bomb.
-Here is more human readable code:
-<code bash>
-bomb() {
- bomb | bomb &
-}; bomb
-</code>
-Properly configured Linux / UNIX box should not go down when fork() bomb sets off.
-==== Extra ====
-Perl exmaple:
-<code perl>
-perl -e "fork while fork" &
-</code>
-Python example:
-<code python>
-import os
-  while(1):
-      os.fork()
-</code>
-Windows XP / Vista bat file example:
-<code>
-:bomb
-start %0
-goto bomb
-</code>
-UNIX style for Windows:
-<code>
-%0|%0
-</code>
-C program example:
-<code c>
-#include
- int main() {   while(1)      fork();  }
-</code>
-Plz note that the fork bomb is a form of denial of service, so don’t run on production or unauthorized system.
-==== Fuente ====
-http://www.cyberciti.biz/faq/understanding-bash-fork-bomb/#comment-37097