[SOLVED] confused by set user id

xeveri · 04-29-2014, 03:59 AM

I am new to linux and i choose slackware.
When learning set user id,i am confused about it.So i decide to try with a script.

#!/bin/bash
touch tryset

It was written by root in the home directory of user guo. After changing mod, it was
-rwsr--r-x root root ...
When running by root,the attribute of tryset is root.The attribute of it is guo when running by user guo.
I think the file attribute is root when running by guo due to setting user id...So what is the case ?
It seems the script must have x permission for others.

saulgoode · 04-29-2014, 05:24 AM

Quote:

Originally Posted by xeveri

I am new to linux and i choose slackware.
When learning set user id,i am confused about it.So i decide to try with a script.

For security reasons, SUID is disabled/ignored for shell scripts. I believe this is configurable when you compile the kernel, so caveat lector for other distros.

If you were to compile the following C code, and set the permissions of the resulting binary for SUID, things will work as one'd expect.

Code:

#include <stdio.h>

main()
{
   FILE *fp;
   unlink("/tmp/test.txt");
   fp = fopen("/tmp/test.txt", "w");
   fclose(fp);
}

Code:

root@faraday:~# gcc test.c -o /tmp/testsuid 
root@faraday:~# chmod u+s -v /tmp/testsuid 
mode of '/tmp/testsuid' changed from 0755 (rwxr-xr-x) to 4755 (rwsr-xr-x)

xeveri · 04-29-2014, 07:58 AM

Thanks for your help. I'll test the example you give up.