topic Re: C API for removing a user in Operating System - HP-UX

C API for removing a user

Helen Gao — Thu, 28 Feb 2002 20:58:14 GMT

Dear all,

Is there a C API for removing a user?

Thanks.

Re: C API for removing a user

A. Clay Stephenson — Thu, 28 Feb 2002 21:16:51 GMT

Hi:

By far the easiest method is to call the userdel command via system. e.g.

char *the_user;
int status;
char s_cmd[256];

(void) sprintf(s_cmd,"userdel -r %s",the_user);
cc = system(userdel);

Clay

Re: C API for removing a user

Eric Ladner — Thu, 28 Feb 2002 22:21:21 GMT

I would put an absolute path on that userdel for security purposes.

You might want to consider protecting that from buffer overflows too.

Re: C API for removing a user

Helen Gao — Fri, 01 Mar 2002 15:45:43 GMT

Thanks, guys.

>>You might want to consider protecting that >>from buffer overflows too.

Eric, could you give me more detail on this?

Re: C API for removing a user

A. Clay Stephenson — Fri, 01 Mar 2002 16:03:31 GMT

Hi:

All is is saying is that my baby example was not very robust.

char *the_user;
int status;
char s_cmd[256];

(void) sprintf(s_cmd,"userdel -r s",the_user);
cc = system(userdel);

The problem is that is is conceivable (though very unlikely) that the length of the command might exceed the size of s_cmd [256] characters - a buffer overflow.

# ----------------------------------------
The nit-picky though really not need method:

#define CMD "/sbin/userdel -r "

extern int errno;

int remove_user(char *the_user)
{
int cc = 0;

if (the_user != NULL)
{
int len = 4; /* cushion */
char *s_cmd = NULL;

len += (int) strlen(the_user);
len += (int) strlen(CMD);
s_cmd = (char *) malloc(size_t) len);
if (s_cmd != NULL)
{
(void) sprintf(s_cmd,
"%s %s",CMD,the_user);
cc = system(s_cmd);
free ((void *) s_cmd));
}
else cc = (errno != 0) ? errno : -2;
}
else cc = -1;
return(cc);
} /* remove_user */

-----------------------------------------

cc = remove_user("clay");

Barring any typo's that should be a fully robust version. In real life, as long as you make sure that the length of the user name is no more than ~220 the baby example will be perfectly robust.

Regards, Clay