optionally use PAM

Signed-off-by: Mattias Andrée <maandree@operamail.com>

2 files changed, 314 insertions, 0 deletions

diff --git a/src/auth/pam.c b/src/auth/pam.c
new file mode 100644
index 0000000..e02aed1
--- /dev/null
+++ b/src/auth/pam.c
@@ -0,0 +1,258 @@
+/**
+ * cerberus – Minimal login program
+ * 
+ * Copyright © 2013  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * 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 <stdio.h>
+#include <unistd.h>
+#include <signal.h>
+#include <string.h>
+#include <security/pam_appl.h>
+#include <security/pam_misc.h>
+
+#include "../config.h"
+
+#include "pam.h"
+
+
+#define __failed(RC)  ((RC) != PAM_SUCCESS)
+
+
+void quit_pam(int sig);
+
+int conv_pam(int num_msg, const struct pam_message** msg, struct pam_response** resp, void* appdata_ptr);
+
+
+/**
+ * Old signal action for SIGHUP
+ */
+struct sigaction signal_action_hup;
+
+/**
+ * Old signal action for SIGTERM
+ */
+struct sigaction signal_action_term;
+
+/**
+ * The process ID of the child process, 0 if none
+ */
+extern pid_t child_pid;
+
+/**
+ * The PAM handle
+ */
+static pam_handle_t* handle = NULL;
+
+/**
+ * The PAM convention
+ */
+static struct pam_conv conv = { conv_pam, NULL };
+
+/**
+ * Whether the user was auto-authenticated
+ */
+static char auto_authenticated = 1;
+
+/**
+ * Function that can be used to read a passphrase from the terminal
+ */
+static char* (*passphrase_reader)(void) = NULL;
+
+
+/**
+ * Exit if a PAM instruction failed
+ * 
+ * @param  rc  What the PAM instruction return
+ */
+static void do_pam(int rc)
+{
+  if (__failed(rc))
+    {
+      const char* msg = pam_strerror(handle, rc);
+      if (msg)
+	fprintf(stderr, "%s\n", msg);
+      pam_end(handle, rc);
+      sleep(ERROR_SLEEP);
+      _exit(1);
+    }
+}
+
+
+/**
+ * Initialise PAM
+ * 
+ * @param  remote    The remote computer, {@code NULL} for local login
+ * @param  username  The username of the user to log in to
+ * @param  reader    Function that can be used to read a passphrase from the terminal
+ */
+void initialise_pam(char* remote, char* username, char* (*reader)(void))
+{
+  passphrase_reader = reader;
+  
+  if (pam_start(remote ? "remote" : "local", username, &conv, &handle) != PAM_SUCCESS)
+    {
+      fprintf(stderr, "Cannot initialise PAM\n");
+      sleep(ERROR_SLEEP);
+      _exit(1);
+    }
+  
+  do_pam(pam_set_item(handle, PAM_RHOST, remote ?: "localhost"));
+  do_pam(pam_set_item(handle, PAM_TTY, ttyname(STDIN_FILENO) ?: "(none)"));
+}
+
+
+/**
+ * Verify that the account may be used
+ */
+void verify_account_pam(void)
+{
+  /* FIXME freezes */
+  /*
+  int rc = pam_acct_mgmt(handle, 0);
+  if (rc == PAM_NEW_AUTHTOK_REQD)
+    rc = pam_chauthtok(handle, PAM_CHANGE_EXPIRED_AUTHTOK);
+  do_pam(rc);
+  */
+}
+
+
+/**
+ * Open PAM session
+ */
+void open_session_pam(void)
+{
+  int rc;
+  char** env;
+  struct sigaction signal_action;
+  
+  do_pam(pam_setcred(handle, PAM_ESTABLISH_CRED));
+  
+  if (__failed(rc = pam_open_session(handle, 0)))
+    {
+      pam_setcred(handle, PAM_DELETE_CRED);
+      do_pam(rc);
+    }
+  
+  if (__failed(rc = pam_setcred(handle, PAM_REINITIALIZE_CRED)))
+    {
+      pam_close_session(handle, 0);
+      do_pam(rc);
+    }
+  
+  memset(&signal_action, 0, sizeof(signal_action));
+  signal_action.sa_handler = SIG_IGN;
+  sigaction(SIGINT, &signal_action, NULL);
+  sigaction(SIGHUP, &signal_action, &signal_action_hup);
+  signal_action.sa_handler = quit_pam;
+  sigaction(SIGHUP, &signal_action, NULL);
+  sigaction(SIGTERM, &signal_action, &signal_action_term);
+  
+  for (env = pam_getenvlist(handle); env && *env; env++)
+    if (putenv(*env))
+      {
+	pam_setcred(handle, PAM_DELETE_CRED);
+	pam_end(handle, pam_close_session(handle, 0));
+	sleep(ERROR_SLEEP);
+	_exit(1);
+      }
+}
+
+
+/**
+ * Close PAM session
+ */
+void close_session_pam(void)
+{
+  sigaction(SIGHUP, &signal_action_hup, NULL);
+  sigaction(SIGTERM, &signal_action_term, NULL);
+  
+  pam_setcred(handle, PAM_DELETE_CRED);
+  pam_end(handle, pam_close_session(handle, 0));
+}
+
+
+/**
+ * Signal handler for cleanly exit PAM session
+ * 
+ * @param  sig  The received signal
+ */
+void quit_pam(int sig)
+{
+  if (child_pid)
+    kill(-child_pid, sig);
+  if (sig == SIGTERM)
+    kill(-child_pid, SIGHUP);
+  
+  pam_setcred(handle, PAM_DELETE_CRED);
+  pam_end(handle, pam_close_session(handle, 0));
+  
+  _exit(sig);
+}
+
+
+/**
+ * Perform token authentication
+ * 
+ * @return  Whether the user got automatically authenticated
+ */
+char authenticate_pam(void)
+{
+  int rc;
+  
+  if (__failed(rc = pam_authenticate(handle, 0)))
+    {
+      printf("Incorrect passphrase\n");
+      pam_end(handle, rc);
+      sleep(FAILURE_SLEEP);
+      _exit(1);
+    }
+  
+  return auto_authenticated;
+}
+
+
+/**
+ * Callback function for converation between PAM this application
+ * 
+ * @param   num_msg      Number of pointers in the array `msg`
+ * @param   msg          Message from PAM
+ * @param   resp         Pointer to responses to PAM for by index corresponding messages
+ * @param   appdata_ptr  (Not used)
+ * @return               `PAM_SUCCESS`, `PAM_CONV_ERR` or `PAM_BUF_ERR`
+ */
+int conv_pam(int num_msg, const struct pam_message** msg, struct pam_response** resp, void* appdata_ptr)
+{
+  int i;
+  
+  (void) appdata_ptr;
+  
+  *resp = calloc(num_msg, sizeof(struct pam_response));
+  
+  for (i = 0; i < num_msg; i++)
+    {
+      ((*resp) + i)->resp = NULL;
+      ((*resp) + i)->resp_retcode = 0;
+      
+      if ((**(msg + i)).msg_style == PAM_PROMPT_ECHO_OFF)
+	{
+	  (*resp + i)->resp = passphrase_reader();
+	  auto_authenticated = 0;
+	}
+    }
+  
+  return PAM_SUCCESS;
+}
+
diff --git a/src/auth/pam.h b/src/auth/pam.h
new file mode 100644
index 0000000..ee766df
--- /dev/null
+++ b/src/auth/pam.h
@@ -0,0 +1,56 @@
+/**
+ * cerberus – Minimal login program
+ * 
+ * Copyright © 2013  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * 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/>.
+ */
+#ifndef __PAM_H__
+#define __PAM_H__
+
+
+/**
+ * Initialise PAM
+ * 
+ * @param  remote    The remote computer, {@code NULL} for local login
+ * @param  username  The username of the user to log in to
+ * @param  reader    Function that can be used to read a passphrase from the terminal
+ */
+void initialise_pam(char* remote, char* username, char* (*reader)(void));
+
+/**
+ * Verify that the account may be used
+ */
+void verify_account_pam(void);
+
+/**
+ * Open PAM session
+ */
+void open_session_pam(void);
+
+/**
+ * Close PAM session
+ */
+void close_session_pam(void);
+
+/**
+ * Perform token authentication
+ * 
+ * @return  Whether the user got automatically authenticated
+ */
+char authenticate_pam(void);
+
+
+#endif
+