From ad6aa21c43bb87c917e21416f3ba448b634a98f8 Mon Sep 17 00:00:00 2001 From: Geoff Greer Date: Thu, 12 Apr 2018 17:38:24 -0700 Subject: [PATCH] swaylock: Securely zero-out password. - Replace char* with static array. Any chars > 1024 will be discarded. - mlock() password buffer so it can't be written to swap. - Clear password buffer after auth succeeds or fails. This is basically the same treatment I gave the 0.15 branch in https://github.com/swaywm/sway/pull/1519 --- include/swaylock/swaylock.h | 3 +-- swaylock/main.c | 13 +++++++++++ swaylock/password.c | 44 +++++++++++++++++-------------------- 3 files changed, 34 insertions(+), 26 deletions(-) diff --git a/include/swaylock/swaylock.h b/include/swaylock/swaylock.h index 173e8b12..ed9fea19 100644 --- a/include/swaylock/swaylock.h +++ b/include/swaylock/swaylock.h @@ -24,9 +24,8 @@ struct swaylock_args { }; struct swaylock_password { - size_t size; size_t len; - char *buffer; + char buffer[1024]; }; struct swaylock_state { diff --git a/swaylock/main.c b/swaylock/main.c index 4c6b44c6..200c1b5f 100644 --- a/swaylock/main.c +++ b/swaylock/main.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include @@ -18,10 +19,15 @@ #include "background-image.h" #include "pool-buffer.h" #include "cairo.h" +#include "log.h" #include "util.h" #include "wlr-input-inhibitor-unstable-v1-client-protocol.h" #include "wlr-layer-shell-unstable-v1-client-protocol.h" +void sway_terminate(int exit_code) { + exit(exit_code); +} + static void daemonize() { int fds[2]; if (pipe(fds) != 0) { @@ -236,6 +242,13 @@ int main(int argc, char **argv) { } } +#ifdef __linux__ + // Most non-linux platforms require root to mlock() + if (mlock(state.password.buffer, sizeof(state.password.buffer)) != 0) { + sway_abort("Unable to mlock() password memory."); + } +#endif + wl_list_init(&state.surfaces); state.xkb.context = xkb_context_new(XKB_CONTEXT_NO_FLAGS); state.display = wl_display_connect(NULL); diff --git a/swaylock/password.c b/swaylock/password.c index 1839f991..c8df3de8 100644 --- a/swaylock/password.c +++ b/swaylock/password.c @@ -1,7 +1,9 @@ +#define _XOPEN_SOURCE 500 #include #include #include #include +#include #include #include #include @@ -20,7 +22,7 @@ static int function_conversation(int num_msg, const struct pam_message **msg, switch (msg[i]->msg_style) { case PAM_PROMPT_ECHO_OFF: case PAM_PROMPT_ECHO_ON: - pam_reply[i].resp = pw->buffer; + pam_reply[i].resp = strdup(pw->buffer); // PAM clears and frees this break; case PAM_ERROR_MSG: case PAM_TEXT_INFO: @@ -30,6 +32,16 @@ static int function_conversation(int num_msg, const struct pam_message **msg, return PAM_SUCCESS; } +void clear_password_buffer(struct swaylock_password *pw) { + // Use volatile keyword so so compiler can't optimize this out. + volatile char *buffer = pw->buffer; + volatile char zero = '\0'; + for (size_t i = 0; i < sizeof(buffer); ++i) { + buffer[i] = zero; + } + pw->len = 0; +} + static bool attempt_password(struct swaylock_password *pw) { struct passwd *passwd = getpwuid(getuid()); char *username = passwd->pw_name; @@ -38,6 +50,7 @@ static bool attempt_password(struct swaylock_password *pw) { }; pam_handle_t *local_auth_handle = NULL; int pam_err; + // TODO: only call pam_start once. keep the same handle the whole time if ((pam_err = pam_start("swaylock", username, &local_conversation, &local_auth_handle)) != PAM_SUCCESS) { wlr_log(L_ERROR, "PAM returned error %d", pam_err); @@ -46,18 +59,15 @@ static bool attempt_password(struct swaylock_password *pw) { wlr_log(L_ERROR, "pam_authenticate failed"); goto fail; } + // TODO: only call pam_end once we succeed at authing. refresh tokens beforehand if ((pam_err = pam_end(local_auth_handle, pam_err)) != PAM_SUCCESS) { wlr_log(L_ERROR, "pam_end failed"); goto fail; } - // PAM frees this - pw->buffer = NULL; - pw->len = pw->size = 0; + clear_password_buffer(pw); return true; fail: - // PAM frees this - pw->buffer = NULL; - pw->len = pw->size = 0; + clear_password_buffer(pw); return false; } @@ -70,24 +80,10 @@ static bool backspace(struct swaylock_password *pw) { } static void append_ch(struct swaylock_password *pw, uint32_t codepoint) { - if (!pw->buffer) { - pw->size = 8; - if (!(pw->buffer = malloc(pw->size))) { - // TODO: Display error - return; - } - pw->buffer[0] = 0; - } size_t utf8_size = utf8_chsize(codepoint); - if (pw->len + utf8_size + 1 >= pw->size) { - size_t size = pw->size * 2; - char *buffer = realloc(pw->buffer, size); - if (!buffer) { - // TODO: Display error - return; - } - pw->size = size; - pw->buffer = buffer; + if (pw->len + utf8_size + 1 >= sizeof(pw->buffer)) { + // TODO: Display error + return; } utf8_encode(&pw->buffer[pw->len], codepoint); pw->buffer[pw->len + utf8_size] = 0;