This involves setuid'ing swaylock, which then forks and drops perms on the parent process. The child process remains root and listens on a pipe for requests to validate passwords against /etc/shadow.master
Drew DeVault
6 years ago
parent
58af001517
commit
c977349120
@ -0,0 +1,62 @@
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#define _XOPEN_SOURCE 500
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#include <pwd.h>
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#include <security/pam_appl.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <wlr/util/log.h>
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#include "swaylock/swaylock.h"
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void initialize_pw_backend(void) {
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// TODO: only call pam_start once. keep the same handle the whole time
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}
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static int function_conversation(int num_msg, const struct pam_message **msg,
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struct pam_response **resp, void *data) {
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struct swaylock_password *pw = data;
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/* PAM expects an array of responses, one for each message */
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struct pam_response *pam_reply = calloc(
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num_msg, sizeof(struct pam_response));
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*resp = pam_reply;
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for (int i = 0; i < num_msg; ++i) {
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switch (msg[i]->msg_style) {
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case PAM_PROMPT_ECHO_OFF:
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case PAM_PROMPT_ECHO_ON:
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pam_reply[i].resp = strdup(pw->buffer); // PAM clears and frees this
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break;
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case PAM_ERROR_MSG:
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case PAM_TEXT_INFO:
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break;
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}
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}
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return PAM_SUCCESS;
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}
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bool attempt_password(struct swaylock_password *pw) {
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struct passwd *passwd = getpwuid(getuid());
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char *username = passwd->pw_name;
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const struct pam_conv local_conversation = {
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function_conversation, pw
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};
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pam_handle_t *local_auth_handle = NULL;
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int pam_err;
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if ((pam_err = pam_start("swaylock", username,
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&local_conversation, &local_auth_handle)) != PAM_SUCCESS) {
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wlr_log(WLR_ERROR, "PAM returned error %d", pam_err);
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}
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if ((pam_err = pam_authenticate(local_auth_handle, 0)) != PAM_SUCCESS) {
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wlr_log(WLR_ERROR, "pam_authenticate failed");
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goto fail;
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}
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// TODO: only call pam_end once we succeed at authing. refresh tokens beforehand
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if ((pam_err = pam_end(local_auth_handle, pam_err)) != PAM_SUCCESS) {
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wlr_log(WLR_ERROR, "pam_end failed");
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goto fail;
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}
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clear_password_buffer(pw);
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return true;
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fail:
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clear_password_buffer(pw);
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return false;
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}
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@ -0,0 +1,128 @@
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#define _XOPEN_SOURCE
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#include <pwd.h>
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#include <shadow.h>
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#include <stdbool.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <wlr/util/log.h>
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#include "swaylock/swaylock.h"
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static int comm[2][2];
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void run_child(void) {
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/* This code runs as root */
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struct passwd *pwent = getpwuid(getuid());
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if (!pwent) {
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wlr_log_errno(WLR_ERROR, "failed to getpwuid");
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exit(EXIT_FAILURE);
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}
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char *encpw = pwent->pw_passwd;
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if (strcmp(encpw, "x") == 0) {
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struct spwd *swent = getspnam(pwent->pw_name);
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if (!swent) {
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wlr_log_errno(WLR_ERROR, "failed to getspnam");
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exit(EXIT_FAILURE);
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}
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encpw = swent->sp_pwdp;
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}
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wlr_log(WLR_DEBUG, "prepared to authorize user %s", pwent->pw_name);
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size_t size;
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char *buf;
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while (1) {
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ssize_t amt;
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amt = read(comm[0][0], &size, sizeof(size));
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if (amt == 0) {
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break;
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} else if (amt < 0) {
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wlr_log_errno(WLR_ERROR, "read pw request");
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}
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wlr_log(WLR_DEBUG, "received pw check request");
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buf = malloc(size);
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if (!buf) {
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wlr_log_errno(WLR_ERROR, "failed to malloc pw buffer");
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exit(EXIT_FAILURE);
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}
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size_t offs = 0;
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do {
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amt = read(comm[0][0], &buf[offs], size - offs);
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if (amt <= 0) {
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wlr_log_errno(WLR_ERROR, "failed to read pw");
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exit(EXIT_FAILURE);
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}
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offs += (size_t)amt;
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} while (offs < size);
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bool result = false;
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char *c = crypt(buf, encpw);
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if (c == NULL) {
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wlr_log_errno(WLR_ERROR, "crypt");
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}
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result = strcmp(c, encpw) == 0;
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if (write(comm[1][1], &result, sizeof(result)) != sizeof(result)) {
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wlr_log_errno(WLR_ERROR, "failed to write pw check result");
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exit(EXIT_FAILURE);
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}
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free(buf);
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}
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exit(EXIT_SUCCESS);
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}
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void initialize_pw_backend(void) {
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if (geteuid() != 0) {
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wlr_log(WLR_ERROR, "swaylock needs to be setuid to read /etc/shadow");
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exit(EXIT_FAILURE);
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}
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if (pipe(comm[0]) != 0) {
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wlr_log_errno(WLR_ERROR, "failed to create pipe");
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exit(EXIT_FAILURE);
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}
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if (pipe(comm[1]) != 0) {
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wlr_log_errno(WLR_ERROR, "failed to create pipe");
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exit(EXIT_FAILURE);
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}
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pid_t child = fork();
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if (child == 0) {
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close(comm[0][1]);
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close(comm[1][0]);
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run_child();
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} else if (child < 0) {
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wlr_log_errno(WLR_ERROR, "failed to fork");
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exit(EXIT_FAILURE);
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}
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close(comm[0][0]);
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close(comm[1][1]);
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if (setgid(getgid()) != 0) {
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wlr_log_errno(WLR_ERROR, "Unable to drop root");
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exit(EXIT_FAILURE);
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}
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if (setuid(getuid()) != 0) {
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wlr_log_errno(WLR_ERROR, "Unable to drop root");
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exit(EXIT_FAILURE);
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}
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}
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bool attempt_password(struct swaylock_password *pw) {
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bool result = false;
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size_t len = pw->len + 1;
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size_t offs = 0;
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if (write(comm[0][1], &len, sizeof(len)) < 0) {
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wlr_log_errno(WLR_ERROR, "Failed to request pw check");
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goto ret;
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}
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do {
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ssize_t amt = write(comm[0][1], &pw->buffer[offs], len - offs);
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if (amt < 0) {
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wlr_log_errno(WLR_ERROR, "Failed to write pw buffer");
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goto ret;
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}
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offs += amt;
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} while (offs < len);
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if (read(comm[1][0], &result, sizeof(result)) != sizeof(result)) {
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wlr_log_errno(WLR_ERROR, "Failed to read pw result");
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goto ret;
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}
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wlr_log(WLR_DEBUG, "pw result: %d", result);
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ret:
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clear_password_buffer(pw);
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return result;
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}
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