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Lock the password buffer in memory, clear it in RAM after verifying

pull/1/head
Michael Stapelberg 2012-01-03 16:17:58 +00:00
parent 2dd03ce7db
commit 52f96e78f2
1 changed files with 28 additions and 2 deletions
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30
i3lock.c
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@ -24,6 +24,7 @@
#include <string.h>
#include <math.h>
#include <ev.h>
#include <sys/mman.h>
#ifndef NOLIBCAIRO
@ -51,7 +52,7 @@ static xcb_key_symbols_t *symbols;
static xcb_screen_t *scr;
static pam_handle_t *pam_handle;
static int input_position = 0;
/* holds the password you enter (in UTF-8) */
/* Holds the password you enter (in UTF-8). */
static char password[512];
static bool modeswitch_active = false;
static bool iso_level3_shift_active = false;
@ -91,6 +92,23 @@ static cairo_surface_t *img = NULL;
static bool tile = false;
#endif
/*
* Clears the memory which stored the password to be a bit safer against
* cold-boot attacks.
*
*/
static void clear_password_memory() {
/* A volatile pointer to the password buffer to prevent the compiler from
* optimizing this out. */
volatile char *vpassword = password;
for (int c = 0; c < sizeof(password); c++)
/* We store a non-random pattern which consists of the (irrelevant)
* index plus (!) the value of the beep variable. This prevents the
* compiler from optimizing the calls away, since the value of 'beep'
* is not known at compile-time. */
vpassword[c] = c + (int)beep;
}
/*
* Draws global image with fill color onto a pixmap with the given
* resolution and returns it.
@ -330,6 +348,7 @@ static void input_done() {
if (pam_authenticate(pam_handle, 0) == PAM_SUCCESS) {
printf("successfully authenticated\n");
clear_password_memory();
exit(0);
}
@ -458,6 +477,7 @@ static void handle_key_press(xcb_key_press_event_t *event) {
input_done();
case XK_Escape:
input_position = 0;
clear_password_memory();
password[input_position] = '\0';
return;
@ -809,7 +829,13 @@ int main(int argc, char *argv[]) {
/* Initialize PAM */
ret = pam_start("i3lock", username, &conv, &pam_handle);
if (ret != PAM_SUCCESS)
errx(EXIT_FAILURE, "PAM: %s\n", pam_strerror(pam_handle, ret));
errx(EXIT_FAILURE, "PAM: %s", pam_strerror(pam_handle, ret));
/* Lock the area where we store the password in memory, we don’t want it to
* be swapped to disk. Since Linux 2.6.9, this does not require any
* privileges, just enough bytes in the RLIMIT_MEMLOCK limit. */
if (mlock(password, sizeof(password)) != 0)
err(EXIT_FAILURE, "Could not lock page in memory, check RLIMIT_MEMLOCK");
/* Initialize connection to X11 */
if ((conn = xcb_connect(NULL, &screen)) == NULL ||