how to write a wrapper c code to return uid using getuid() function

pwd · #1 (**permalink**) 05-11-2008

And how to use setuid() ?
thanks

jim mcnamara · #2 (**permalink**) 05-12-2008

Code:

#include <unistd.h>
uid_t myuid(void)
{
    return getuid();
}

No offense meant, but setuid is a major security risk. Don't go implementing your code on your system unless it is a home desktop that can be trashed.

setuid requires either root or the so-called sticky bit set to allow the program to change it's username.

It may seem simple but there is a lot to writing a setuid program:

http://nob.cs.ucdavis.edu/bishop/sec...sproglogin.pdf

ramen_noodle · #3 (**permalink**) 05-12-2008

setuid() is pretty integral to a safe unix process.
One basic mode is for a root privileged parent to acquire
resources only it can handle (ports < 1024) and then delegate service to setuid(> 0) children/threads, ala OpenSSH and many other pieces of software via IPC.

Given it's not easy to do securely and does pose a considerable security issue: mostly races and various abuses of unsafe programing practices in the privileged process.

pwd · #4 (**permalink**) 05-13-2008

thanks jim mcnamara,
i want catch value of getuid() to put into a logfile. How to do it?

jim mcnamara · #5 (**permalink**) 05-13-2008

one way:

Code:

id >> logfile

c code

Code:

/* myid.c */
#include <unistd.h>
uid_t myuid(void)
{
    return getuid();
}

int main()
{
     printf("%d\n", myuid() );
     return 0;
}

cc myid.c -o myid

in your script

Code:

myid >> logfile

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