Crash of putpwent API.

Question

Hi,
I am using the putpwent and putspent API for editing the /etc/passwd and /etc/shadow file.
I have a funtion which takes userName and password
OsCreateUser (char* userName , char* passwd , uid_t uid)
There are two scenarious
(i) I am dynamically allocating memory for
struct passwd and
struct spwd
in this case I my code is like
ptr = (struct passwd*) malloc (sizeof (struct passwd) );
sptr = (struct spwd*) malloc (sizeof (struct spwd) );
if ( (fp = fopen ("/etc/passwd","a")) == NULL){
return (errno);
ptr->pw_name = strdup(userName);
ptr->pw_passwd = strdup("x");
ptr->pw_gid = 1;
ptr->pw_gecos = strdup("User");
ptr->pw_uid = uid;
ptr->pw_dir = strdup("/false");
ptr->pw_shell = strdup("/bin/false");
putpwent (ptr,fp);
fclose (fp );
if ( (fp = fopen ( "/etc/shadow","a")) == NULL ){
return (errno);
/*Setting the default values */
sptr->sp_namp = strdup(userName);
sptr->sp_pwdp = strdup("345dfkjgh84");
sptr->sp_lstchg = 14202;
sptr->sp_min = -1;
sptr->sp_max = -1;
sptr->sp_warn = -1;
sptr->sp_inact = -1;
sptr->sp_expire = -1;
sptr->sp_flag = 0;
putspent (sptr,fp);
if ( (fclose(fp) )!= 0 ){
return (errno);
there is a code to free the memory.
======================================
And after when the fuction is called again then i allocate memory for ptr and sptr pointers.
========================================================================
The problem is that if I call this function many times then this API putpwet crashes.

Answer 1

Have you run it in a debugger and see where it dies? putpwent basically does a bunch of fprintfs, so if it dies, either it's being passed bogus parameters, or malloc was screwed up (like freeing something twice). You could try running your app with watchmalloc (man watchmalloc) with MALLOC_DEBUG=RW and see if it complains.