C API for removing a user

[Helen Gao]

Dear all,

Is there a C API for removing a user?

Thanks.

[A. Clay Stephenson · Accepted solution]

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

[Eric Ladner]

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

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

[Helen Gao]

Thanks, guys.

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

Eric, could you give me more detail on this?

[A. Clay Stephenson]

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