--- /dev/null
+
+ Support to pass the password via a pipe to the pppd
+ ---------------------------------------------------
+
+ Arvin Schnell <arvin@suse.de>
+ 2002-02-08
+
+
+1. Introduction
+---------------
+
+Normally programs like wvdial or kppp read the online password from their
+config file and store them in the pap- and chap-secrets before they start the
+pppd and remove them afterwards. Sure they need special privileges to do so.
+
+The passwordfd feature offers a simpler and more secure solution. The program
+that starts the pppd opens a pipe and writes the password into it. The pppd
+simply reads the password from that pipe.
+
+This methods is used for quiet a while on SuSE Linux by the programs wvdial,
+kppp and smpppd.
+
+
+2. Example
+----------
+
+Here is a short C program that uses the passwordfd feature. It starts the pppd
+to buildup a pppoe connection.
+
+
+--snip--
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <string.h>
+#include <paths.h>
+
+#ifndef _PATH_PPPD
+#define _PATH_PPPD "/usr/sbin/pppd"
+#endif
+
+
+// Of course these values can be read from a configuration file or
+// entered in a graphical dialog.
+char *device = "eth0";
+char *username = "1122334455661122334455660001@t-online.de";
+char *password = "hello";
+
+pid_t pid = 0;
+
+
+void
+sigproc (int src)
+{
+ fprintf (stderr, "Sending signal %d to pid %d\n", src, pid);
+ kill (pid, src);
+ exit (EXIT_SUCCESS);
+}
+
+
+void
+sigchild (int src)
+{
+ fprintf (stderr, "Daemon died\n");
+ exit (EXIT_SUCCESS);
+}
+
+
+int
+start_pppd ()
+{
+ signal (SIGINT, &sigproc);
+ signal (SIGTERM, &sigproc);
+ signal (SIGCHLD, &sigchild);
+
+ pid = fork ();
+ if (pid < 0) {
+ fprintf (stderr, "unable to fork() for pppd: %m\n");
+ return 0;
+ }
+
+ if (pid == 0) {
+
+ int i, pppd_argc = 0;
+ char *pppd_argv[20];
+ char buffer[32] = "";
+ int pppd_passwdfd[2];
+
+ for (i = 0; i < 20; i++)
+ pppd_argv[i] = NULL;
+
+ pppd_argv[pppd_argc++] = "pppd";
+
+ pppd_argv[pppd_argc++] = "call";
+ pppd_argv[pppd_argc++] = "pwfd-test";
+
+ // The device must be after the call, since the call loads the plugin.
+ pppd_argv[pppd_argc++] = device;
+
+ pppd_argv[pppd_argc++] = "user";
+ pppd_argv[pppd_argc++] = username;
+
+ // Open a pipe to pass the password to pppd.
+ if (pipe (pppd_passwdfd) == -1) {
+ fprintf (stderr, "pipe failed: %m\n");
+ exit (EXIT_FAILURE);
+ }
+
+ // Of course this only works it the password is shorter
+ // than the pipe buffer. Otherwise you have to fork to
+ // prevent that your main program blocks.
+ write (pppd_passwdfd[1], password, strlen (password));
+ close (pppd_passwdfd[1]);
+
+ // Tell the pppd to read the password from the fd.
+ pppd_argv[pppd_argc++] = "passwordfd";
+ snprintf (buffer, 32, "%d", pppd_passwdfd[0]);
+ pppd_argv[pppd_argc++] = buffer;
+
+ if (execv (_PATH_PPPD, (char **) pppd_argv) < 0) {
+ fprintf (stderr, "cannot execl %s: %m\n", _PATH_PPPD);
+ exit (EXIT_FAILURE);
+ }
+ }
+
+ pause ();
+
+ return 1;
+}
+
+
+int
+main (int argc, char **argv)
+{
+ if (start_pppd ())
+ exit (EXIT_SUCCESS);
+
+ exit (EXIT_FAILURE);
+}
+
+---snip---
+
+
+Copy this file to /etc/ppp/peers/pwfd-test. The plugins can't be loaded on the
+command line (unless you are root) since the plugin option is privileged.
+
+
+---snip---
+
+#
+# PPPoE plugin for kernel 2.4
+#
+plugin pppoe.so
+
+#
+# This plugin enables us to pipe the password to pppd, thus we don't have
+# to fiddle with pap-secrets and chap-secrets. The user is also passed
+# on the command line.
+#
+plugin passwordfd.so
+
+noauth
+usepeerdns
+defaultroute
+hide-password
+nodetach
+nopcomp
+novjccomp
+noccp
+
+---snip---
+
--- /dev/null
+
+/*
+ * Author: Arvin Schnell <arvin@suse.de>
+ *
+ * This plugin let's you pass the password to the pppd via
+ * a file descriptor. That's easy and secure - no fiddling
+ * with pap- and chap-secrets files.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "pppd.h"
+
+char pppd_version[] = VERSION;
+
+static int passwdfd = -1;
+static char save_passwd[MAXSECRETLEN];
+
+static option_t options[] = {
+ { "passwordfd", o_int, &passwdfd,
+ "Receive password on this file descriptor" },
+ { NULL }
+};
+
+static int pwfd_check (void)
+{
+ return 1;
+}
+
+static int pwfd_passwd (char *user, char *passwd)
+{
+ int readgood, red;
+
+ if (passwdfd == -1)
+ return -1;
+
+ if (passwd == NULL)
+ return 1;
+
+ if (passwdfd == -2) {
+ strcpy (passwd, save_passwd);
+ return 1;
+ }
+
+ readgood = 0;
+ do {
+ red = read (passwdfd, passwd + readgood, MAXSECRETLEN - 1 - readgood);
+ if (red == 0)
+ break;
+ if (red < 0) {
+ error ("Can't read secret from fd\n");
+ readgood = -1;
+ break;
+ }
+ readgood += red;
+ } while (readgood < MAXSECRETLEN - 1);
+
+ close (passwdfd);
+
+ if (readgood < 0)
+ return 0;
+
+ passwd[readgood] = 0;
+ strcpy (save_passwd, passwd);
+ passwdfd = -2;
+
+ return 1;
+}
+
+void plugin_init (void)
+{
+ add_options (options);
+
+ pap_check_hook = pwfd_check;
+ pap_passwd_hook = pwfd_passwd;
+
+ chap_check_hook = pwfd_check;
+ chap_passwd_hook = pwfd_passwd;
+}
projects / ppp.git / commitdiff