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Top Forums Shell Programming and Scripting Passing varibles as a string argument ? Post 302575200 by secops on Monday 21st of November 2011 12:15:54 AM
Old 11-21-2011
Quote:
Originally Posted by mirni
Although this construct will work, I would like to suggest you redesign the script. The reason is security vulnerability that you are implicitly building into it. What if the user runs the script with "./test.sh rm -r /" (don't run this!)? Your script would execute that command obediently.
You'd be better off to stay away from 'eval', if you cannot have total control of the argument of 'eval'. In other words, invoking eval on a user-defined input can be dangerous.

You might want to hard-code the command into your script, and then just pass the argument to it, something like:

Code:
#!/bin/bash
arg=$1
#do whatever
echo $arg

and then call the script with
Code:
./test.sh "$var"

If you can show us a bigger picture of what you are trying to accomplish, we could suggest a better way to implement it.
Thanks for pointing that out.

If the user tried to delete the root directory, wouldn't it stop them because they aren't root?

Basically, I've made a bash script that runs commands passed to it on multiple devices.

Then, for scheduled tasks, I'm having the script be called with commands and variables to facilitate easier management.

The tricky part is making it so a user can do something like ./send-commands devicelist "ssh $username@$device" which I've fixed using the eval method.
 

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SETUID(1)						      General Commands Manual							 SETUID(1)

NAME
setuid - run a command with a different uid. SYNOPSIS
setuid username|uid command [ args ] DESCRIPTION
Setuid changes user id, then executes the specified command. Unlike some versions of su(1), this program doesn't ever ask for a password when executed with effective uid=root. This program doesn't change the environment; it only changes the uid and then uses execvp() to find the command in the path, and execute it. (If the command is a script, execvp() passes the command name to /bin/sh for processing.) For example, setuid some_user $SHELL can be used to start a shell running as another user. Setuid is useful inside scripts that are being run by a setuid-root user -- such as a script invoked with super, so that the script can execute some commands using the uid of the original user, instead of root. This allows unsafe commands (such as editors and pagers) to be used in a non-root mode inside a super script. For example, an operator with permission to modify a certain protected_file could use a super command that simply does: cp protected_file temp_file setuid $ORIG_USER ${EDITOR:-/bin/vi} temp_file cp temp_file protected_file (Note: don't use this example directly. If the temp_file can somehow be replaced by another user, as might be the case if it's kept in a temporary directory, there will be a race condition in the time between editing the temporary file and copying it back to the protected file.) AUTHOR
Will Deich local SETUID(1)
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