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Merge pull request #1519 from ggreer/clear-password-buffer-0.15

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Swaylock: Clear password buffer after use.
This commit is contained in:
Drew DeVault 2017-12-16 21:12:36 -05:00 • committed by GitHub
commit 1263ea6497
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 25 additions and 30 deletions
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55
swaylock/main.c
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@ -7,6 +7,7 @@
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
#include <sys/mman.h>
#include <sys/types.h> #include <sys/types.h>
#include <pwd.h> #include <pwd.h>
#include <getopt.h> #include <getopt.h>
@ -56,8 +57,7 @@ void sway_terminate(int exit_code) {
exit(exit_code); exit(exit_code);
} }
char *password; char password[1024];
int password_size;
enum line_source line_source = LINE_SOURCE_DEFAULT; enum line_source line_source = LINE_SOURCE_DEFAULT;
struct lock_config *init_config() { struct lock_config *init_config() {
@ -115,7 +115,7 @@ int function_conversation(int num_msg, const struct pam_message **msg,
switch (msg[i]->msg_style) { switch (msg[i]->msg_style) {
case PAM_PROMPT_ECHO_OFF: case PAM_PROMPT_ECHO_OFF:
case PAM_PROMPT_ECHO_ON: case PAM_PROMPT_ECHO_ON:
pam_reply[i].resp = password; pam_reply[i].resp = strdup(password); // PAM clears and frees this
break; break;
case PAM_ERROR_MSG: case PAM_ERROR_MSG:
@ -127,9 +127,15 @@ int function_conversation(int num_msg, const struct pam_message **msg,
return PAM_SUCCESS; return PAM_SUCCESS;
} }
/** void clear_password_buffer() {
* Note: PAM will free() 'password' during the process // Use volatile keyword so so compiler can't optimize this out.
*/ volatile char *pw = password;
volatile char zero = '\0';
for (size_t i = 0; i < sizeof(password); ++i) {
pw[i] = zero;
}
}
bool verify_password() { bool verify_password() {
struct passwd *passwd = getpwuid(getuid()); struct passwd *passwd = getpwuid(getuid());
char *username = passwd->pw_name; char *username = passwd->pw_name;
@ -151,8 +157,7 @@ bool verify_password() {
void notify_key(enum wl_keyboard_key_state state, xkb_keysym_t sym, uint32_t code, uint32_t codepoint) { void notify_key(enum wl_keyboard_key_state state, xkb_keysym_t sym, uint32_t code, uint32_t codepoint) {
int redraw_screen = 0; int redraw_screen = 0;
char *password_realloc; size_t i;
int i;
if (state == WL_KEYBOARD_KEY_STATE_PRESSED) { if (state == WL_KEYBOARD_KEY_STATE_PRESSED) {
switch (sym) { switch (sym) {
@ -165,14 +170,14 @@ void notify_key(enum wl_keyboard_key_state state, xkb_keysym_t sym, uint32_t cod
wl_dispatch_events(); wl_dispatch_events();
if (verify_password()) { if (verify_password()) {
clear_password_buffer();
exit(0); exit(0);
} }
render_data.auth_state = AUTH_STATE_INVALID; render_data.auth_state = AUTH_STATE_INVALID;
redraw_screen = 1; redraw_screen = 1;
password_size = 1024; clear_password_buffer();
password = malloc(password_size);
password[0] = '\0'; password[0] = '\0';
break; break;
case XKB_KEY_BackSpace: case XKB_KEY_BackSpace:
@ -207,9 +212,7 @@ void notify_key(enum wl_keyboard_key_state state, xkb_keysym_t sym, uint32_t cod
render_data.auth_state = AUTH_STATE_BACKSPACE; render_data.auth_state = AUTH_STATE_BACKSPACE;
redraw_screen = 1; redraw_screen = 1;
password_size = 1024; clear_password_buffer();
free(password);
password = malloc(password_size);
password[0] = '\0'; password[0] = '\0';
break; break;
} }
@ -218,22 +221,10 @@ void notify_key(enum wl_keyboard_key_state state, xkb_keysym_t sym, uint32_t cod
render_data.auth_state = AUTH_STATE_INPUT; render_data.auth_state = AUTH_STATE_INPUT;
redraw_screen = 1; redraw_screen = 1;
i = strlen(password); i = strlen(password);
if (i + 1 == password_size) { if (i + 1 < sizeof(password)) {
password_size += 1024; password[i] = (char)codepoint;
password_realloc = realloc(password, password_size); password[i + 1] = '\0';
// reset password if realloc fails.
if (password_realloc == NULL) {
password_size = 1024;
free(password);
password = malloc(password_size);
password[0] = '\0';
break;
} else {
password = password_realloc;
}
} }
password[i] = (char)codepoint;
password[i + 1] = '\0';
break; break;
} }
if (redraw_screen) { if (redraw_screen) {
@ -539,8 +530,12 @@ int main(int argc, char **argv) {
sway_abort("Unsupported scaling mode: %s", scaling_mode_str); sway_abort("Unsupported scaling mode: %s", scaling_mode_str);
} }
password_size = 1024; #ifdef __linux__
password = malloc(password_size); // Most non-linux platforms require root to mlock()
if (mlock(password, sizeof(password)) != 0) {
sway_abort("Unable to mlock() password memory.");
}
#endif
password[0] = '\0'; password[0] = '\0';
render_data.surfaces = create_list(); render_data.surfaces = create_list();
if (!socket_path) { if (!socket_path) {