setuid funciton

setuid funciton

[Cihan Kömeçoğlu]

Hello everybody

I have written simple code about usage of setuid. this program file set-user-id bit is on and this process after exec when I execute this program, effective user id and saved-user-id bit will be program-file's user id. this correct?

But the last output when I set uid to 80(www) ,effective user id wasn't 80. Why not? saved set user id is still 80? What is the problem?


I compiled below code with gcc and I set-user-id bit and change own file with this command


Code:
 #include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main(void)
{
  
    printf("Real UID\t= %d\n", getuid());
    printf("Effective UID\t= %d\n", geteuid());
    printf("Real GID\t= %d\n", getgid());
    printf("Effective GID\t= %d\n", getegid());
        
         setuid(1001);
    printf("Real UID\t= %d\n", getuid());
    printf("Effective UID\t= %d\n", geteuid());
    printf("Real GID\t= %d\n", getgid());
    printf("Effective GID\t= %d\n", getegid());

setuid(80);
    printf("Real UID\t= %d\n", getuid());
    printf("Effective UID\t= %d\n", geteuid());
    printf("Real GID\t= %d\n", getgid());
    printf("Effective GID\t= %d\n", getegid());
    return EXIT_SUCCESS;
}gcc setuid-simple.c -o setuid-simple
#[root] chown www setuid-simple
#[root] chmod 4755 setuid-simple

and output with ls command
-rwsr-xr-x 1 www wheel 5708 23 Ara 11:41 setuid-simple


this is program's output:


Quote:
Real UID = 1001
Effective UID = 80
Real GID = 0
Effective GID = 0
/*setuid(1001)*/
Real UID = 1001
Effective UID = 1001
Real GID = 0
Effective GID = 0
/*setuid(80)*/
Real UID = 1001
Effective UID = 1001
Real GID = 0
Effective GID = 0 




-- 
Cihan Kömeçoðlu,
EnderUNIX SDT                         mailto:cihan@enderunix.org

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Re: setuid funciton

[Glynn Clements]

Cihan Kömeçoğlu wrote:

> Hello everybody
> 
> I have written simple code about usage of setuid. this program file
> set-user-id bit is on and this process after exec when I execute this
> program, effective user id and saved-user-id bit will be
> program-file's user id. this correct?
> 
> But the last output when I set uid to 80(www) ,effective user id
> wasn't 80. Why not? saved set user id is still 80? What is the
> problem?
> 
> 
> I compiled below code with gcc and I set-user-id bit and change own
> file with this command

[snip]

It works for me; I get:

Real UID	= 1001
Effective UID	= 80
Real UID	= 1001
Effective UID	= 1001
Real UID	= 1001
Effective UID	= 80

This is with a 2.6.17.13 kernel, compiled from stock sources (no
vendor patches).

If you are using a kernel with additional security features (e.g. 
SELinux, AppArmor etc), it may impose additional restrictions on
setuid(). You could try using setreuid() to swap the real and
effective UIDs, rather than relying upon the saved UID.

-- 
Glynn Clements <glynn@gclements.plus.com>
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Re[2]: setuid funciton

[Cihan Kömeçoğlu]

I understand. Thanks for your answer
I try this code under Freebsd 6.2
and dont give me this output

Wednesday, December 26, 2007, 5:28:08 AM, you wrote:

> Cihan Kömeçoľlu wrote:

>> Hello everybody
>> 
>> I have written simple code about usage of setuid. this program file
>> set-user-id bit is on and this process after exec when I execute this
>> program, effective user id and saved-user-id bit will be
>> program-file's user id. this correct?
>> 
>> But the last output when I set uid to 80(www) ,effective user id
>> wasn't 80. Why not? saved set user id is still 80? What is the
>> problem?
>> 
>> 
>> I compiled below code with gcc and I set-user-id bit and change own
>> file with this command

> [snip]

> It works for me; I get:

> Real UID        = 1001
> Effective UID   = 80
> Real UID        = 1001
> Effective UID   = 1001
> Real UID        = 1001
> Effective UID   = 80

> This is with a 2.6.17.13 kernel, compiled from stock sources (no
> vendor patches).

> If you are using a kernel with additional security features (e.g. 
> SELinux, AppArmor etc), it may impose additional restrictions on
> setuid(). You could try using setreuid() to swap the real and
> effective UIDs, rather than relying upon the saved UID.




-- 
Cihan Kömeçoðlu,
EnderUNIX SDT                           mailto:cihan@enderunix.org

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