/**
* slibc — Yet another C library
* Copyright © 2015, 2016 Mattias Andrée (m@maandree.se)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <termios.h>
#include <string.h>
#include <strings.h>
#include <errno.h>
#include <slibc-alloca.h>
#define t(...) do { if (__VA_ARGS__) goto fail; } while (0)
/**
* This function performs the actual password-reading
* part of `getpass`. It will read into a statically
* allocated buffer until that buffer is full (8196 bytes,
* including termination), and switch to a dynamically
* allocated buffer when the it [the statically allocated
* buffer] is full.
*
* @prarm fd File descriptor to the, already configured,
* controlling terminal.
* @return The entered line. You should override it with zeroes as
* soon as possible to avoid leaving cleartest passphrases
* visible in memory, or potentially stored to unencrypted
* swap. The returned string is statically allocated, and
* should not be deallocated, if the length of the string,
* is (strictly) less than 8196, otherwise it is dynamically
* allocated, and should be deallocated.
*
* @throws Any error specified for malloc(3).
* @throws Any error specified for read(3).
*/
static char* _getpass(int fd)
{
static char pass_s[8196];
char* pass_d = NULL;
size_t ptr_s = 0, ptr_d = 8196, size_d = (8196 << 1);
ssize_t got = 1;
void* new;
/* Read into statically allocated buffer until it is full. */
while (ptr_s < sizeof(pass_s) / sizeof(char))
{
/* Read. */
t (got = read(fd, pass_s + ptr_s, sizeof(pass_s) - ptr_s * sizeof(char)), got < 0);
ptr_s += (size_t)got;
/* End of line? */
if ((got == 0) || (pass_s[ptr_s - 1] == '\n'))
{
pass_s[ptr_s - !!got] = '\0';
return pass_s;
}
}
/* Transfer input to dynamically allocated buffer. */
t (pass_d = secure_realloc(pass_d, size_d * sizeof(char)), pass_d == NULL);
memcpy(pass_d, pass_s, sizeof(pass_s)), explicit_bzero(pass_s, sizeof(pass_s));
/* Read into dynamically allocated buffer. */
for (;;)
{
/* Do we need to grow the buffer? */
if (ptr_d + 1 == size_d)
{
t (new = secure_realloc(pass_d, (size_d <<= 1) * sizeof(char)), new == NULL);
pass_d = new;
}
/* Read. */
t (got = read(fd, pass_d + ptr_d, (size_d - ptr_d - 1) * sizeof(char)), got < 0);
ptr_d += (size_t)got;
/* End of line? */
if ((got == 0) || (pass_d[ptr_d - 1] == '\n'))
{
pass_d[ptr_d - !!got] = '\0';
return pass_d;
}
}
fail:
saved_errno = errno;
explicit_bzero(pass_s, sizeof(pass_s));
secure_free(pass_d);
errno = saved_errno;
return NULL;
}
/**
* Get password input from the terminal.
*
* The exact behaviour of this function depends on the implementations.
* However you can assume that, the controlling terminal (/dev/tty) is
* opened and used for input and output, and that echoing is disabled.
* You cannot assume that arbitrary lengths are supported. However, in
* this implementation, line editing is enabled and arbitrary lengths
* are supported. If the length of the input (excluding termination) is
* less than 8192 a statically allocated string is returned, otherwise
* a dynamically allocated string is returned.
*
* @etymology (Get) (pass)word from terminal!
*
* @param prompt Text to print at the beginning of the line.
* Used to tell the user what is expected of her.
* Must not be `NULL`.
* @return The entered line. You should override it with zeroes as
* soon as possible to avoid leaving cleartest passphrases
* visible in memory, or potentially stored to unencrypted
* swap. The returned string is statically allocated, do
* not deallocate it, unless you know that you are using
* slibc and the length of the string is at least 8192.
* `NULL` on error. If a statically allocated string is
* returned, it will be overwritten at the next call.
*
* @throws Any error specified for open(3).
* @throws Any error specified for malloc(3).
* @throws Any error specified for read(3).
* @throws Any error specified for tcgetattr(3).
* @throws Any error specified for tcsetattr(3).
* @throws Any error specified for tcdrain(3).
*
* @since Always.
*/
char* getpass(const char* prompt)
{
struct termios saved_stty, stty;
char* pass;
int fd = -1, stty_saved = 0, saved_errno;
/* Open controlling terminal. */
t (fd = open("/dev/tty", O_RDWR | O_NOCTTY | O_CLOEXEC), fd < 0);
/* Configure terminal settings. */
t (tcgetattr(fd, &stty));
saved_stty = stty;
stty_saved = 1;
stty.c_lflag = (stty.c_lflag & (tcflag_t)~(ECHO | ISIG )) | (tcflag_t)ICANON;
stty.c_iflag = (stty.c_iflag & (tcflag_t)~(INLCR | IGNCR)) | (tcflag_t)ICRNL;
t (tcsetattr(fd, TCSAFLUSH, &stty));
t (tcdrain(fd));
/* Prompt the user. */
(void) dprintf(fd, "%s", prompt);
/* Get password. */
pass = _getpass(fd);
if (pass == NULL)
goto fail;
/* Move cursor to next line. */
(void) dprintf(fd, "\n");
/* Restore terminal settings. */
(void) tcsetattr(fd, TCSAFLUSH, &saved_stty);
(void) tcdrain(fd);
/* Close controlling terminal. */
close(fd);
return pass;
fail:
saved_errno = errno;
if (fd >= 0)
close(fd);
if (stty_saved)
{
tcsetattr(fd, TCSAFLUSH, &saved_stty);
tcdrain(fd);
}
errno = saved_errno;
return NULL;
}
