Problem - Kevin Tafuro

Once getpass( ) or readpassphrase( ) return successfully, you should perform as
quickly as possible whatever operation you need to perform with the password that
was obtained. Then clear the contents of the returned buffer so that the cleartext
password or passphrase will not be left visible in memory to a potential attacker.
Prompting for a password on Unix without getpass( ) or readpassphrase( )
The function presented in this subsection, spc_read_password( ), requires two arguments.
The first is a prompt to be displayed to the user, and the second is the FILE
object that points to the input source. If the input source is specified as NULL, spc_
read_password( ) will use _PATH_TTY, which is usually defined to be /dev/tty.
The function reads as much data from the input source as memory is available to
hold. It allocates an internal buffer, which grows incrementally as it is filled. If the
function is successful, the return value will be a pointer to this buffer; otherwise, it
will be a NULL pointer.
Note that we use the unbuffered I/O API for reading data from the input source. The
unbuffered read is necessary to avoid potential odd side effects in the I/O. We cannot
use the stream API because there is no way to save and restore the size of the
stream buffer. That is, we cannot know whether the stream was previously buffered.
#include
#include
#include
#include
#include
#include
#define BUF_STEP 1024 /* Allocate this much space for the password, and if it gets
* this long, reallocate twice the space.
* Rinse, lather, repeat.
*/
static unsigned char *read_password(int termfd) {
unsigned char ch, *ret, *tmp;
unsigned long ctr = 0;
if (!(ret = (unsigned char *)malloc(BUF_STEP + 1))) return 0;
for (;;) {
switch (read(termfd, &ch, 1)) {
case 1:
if (ch != '\n') break;
/* FALL THROUGH */
case 0:
ret[ctr] = 0;
return ret;
default:
free(ret);
return 0;
}
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Prompting for a Password | 395