mdw@git.distorted.org.uk Git - shells/blob - chrootsh.c

   1 /* -*-c-*-
   2  *
   3  * $Id: chrootsh.c,v 1.4 1999/04/22 00:30:27 mdw Exp $
   4  *
   5  * Chroot gaol shell
   6  *
   7  * (c) 1999 Mark Wooding
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 /*----- Revision history --------------------------------------------------*
  28  *
  29  * $Log: chrootsh.c,v $
  30  * Revision 1.4  1999/04/22 00:30:27  mdw
  31  * Miscellanous tidying and security fixes.  Lots of thanks due to Clive
  32  * Jones.
  33  *
  34  * Revision 1.3  1999/04/21 22:52:43  mdw
  35  * Added a pile of syslog stuff, so that admins can see what this thing is
  36  * doing.
  37  *
  38  * Revision 1.2  1999/04/21 09:07:55  mdw
  39  * Fiddle with copyright messages so that they're correct.
  40  *
  41  * Revision 1.1.1.1  1999/04/20 00:19:04  mdw
  42  * Initial versions.
  43  *
  44  */
  45
  46 /*----- Header files ------------------------------------------------------*/
  47
  48 #include <errno.h>
  49 #include <stdio.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52
  53 #include <sys/types.h>
  54 #include <unistd.h>
  55 #include <syslog.h>
  56 #include <pwd.h>
  57
  58 extern char **environ;
  59
  60 /*----- Main code ---------------------------------------------------------*/
  61
  62 #ifndef CHROOTSH_PATH
  63 #  define CHROOTSH_PATH "/usr/bin/chrootsh"
  64 #endif
  65
  66 static const char *quis = "chrootsh";
  67
  68 static void *xmalloc(size_t sz)
  69 {
  70   void *p = malloc(sz);
  71   if (!p) {
  72     setuid(getuid());
  73     fprintf(stderr, "%s: not enough memory\n", quis);
  74     exit(EXIT_FAILURE);
  75   }
  76   return (p);
  77 }
  78
  79 static char *xstrdup(const char *p)
  80 {
  81   size_t sz = strlen(p) + 1;
  82   char *q = xmalloc(sz);
  83   memcpy(q, p, sz);
  84   return (q);
  85 }
  86
  87 int main(int argc, char *argv[])
  88 {
  89   struct passwd *pw;
  90   uid_t me = getuid();
  91   char *myname;
  92   char **env;
  93   char **av;
  94
  95   /* --- Resolve the program name --- */
  96
  97   {
  98     char *p, *q;
  99     p = argv[0];
 100     for (q = argv[0]; *q; q++) {
 101       if (*q == '/')
 102         p = q + 1;
 103     }
 104     if (*p == '-')
 105       p++;
 106     quis = p;
 107     openlog(quis, LOG_PID | LOG_NDELAY, LOG_DAEMON);
 108   }
 109
 110   /* --- Check the user is meant to be chrooted --- */
 111
 112   {
 113     uid_t eff = geteuid();
 114
 115     setreuid(eff, me);
 116     pw = getpwuid(me);
 117     if (!pw) {
 118       syslog(LOG_ERR, "executed by non-existant user (uid = %i)", (int)me);
 119       fprintf(stderr, "%s: you don't exist.  Go away.\n", quis);
 120       exit(EXIT_FAILURE);
 121     }
 122     if (strcmp(pw->pw_shell, CHROOTSH_PATH) != 0) {
 123       syslog(LOG_ERR, "executed by non-chrooted user `%s'", pw->pw_name);
 124       fprintf(stderr, "%s: you aren't a chrooted user\n", quis);
 125       exit(EXIT_FAILURE);
 126     }
 127     endpwent();
 128     setreuid(me, eff);
 129   }
 130
 131   /* --- Chroot the user --- */
 132
 133   {
 134     char *p = xstrdup(pw->pw_dir);
 135     char *q = strstr(p, "/./");
 136     if (q)
 137       *q = 0;
 138
 139     if (chdir(p) || chroot(p)) {
 140       int e = errno;
 141       syslog(LOG_ERR, "error entering chroot gaol: %m");
 142       setuid(me);
 143       fprintf(stderr, "%s: couldn't call chroot: %s\n", quis, strerror(e));
 144       exit(EXIT_FAILURE);
 145     }
 146     setuid(me);
 147     free(p);
 148   }
 149
 150   /* --- Read the new password block --- */
 151
 152   myname = xstrdup(pw->pw_name);
 153   pw = getpwnam(myname);
 154   if (!pw) {
 155     syslog(LOG_ERR,
 156            "configuration error: user `%s' not defined in gaol", myname);
 157     fprintf(stderr, "%s: you don't exist in the gaol\n", quis);
 158     exit(EXIT_FAILURE);
 159   }
 160   endpwent();
 161
 162   /* --- Now fiddle with environment strings and suchlike --- */
 163
 164   {
 165     size_t n;
 166     char **homevar = 0;
 167     for (n = 0; environ[n]; n++)
 168       ;
 169     env = xmalloc((n + 1) * sizeof(char *));
 170
 171     for (n = 0; environ[n]; n++) {
 172       if (strncmp(environ[n], "HOME=", 5) == 0) {
 173         char *p = xmalloc(6 + strlen(pw->pw_dir));
 174         sprintf(p, "HOME=%s", pw->pw_dir);
 175         homevar = &env[n];
 176         env[n] = p;
 177       } else if (strncmp(environ[n], "SHELL=", 6) == 0) {
 178         char *p = xmalloc(7 + strlen(pw->pw_shell));
 179         sprintf(p, "SHELL=%s", pw->pw_shell);
 180         env[n] = p;
 181       } else
 182         env[n] = environ[n];
 183     }
 184     env[n] = 0;
 185
 186     /* --- Change directory (again) --- */
 187
 188     if (chdir(pw->pw_dir)) {
 189       if (homevar) {
 190         free(*homevar);
 191         *homevar = "HOME=/";
 192       }
 193       fprintf(stderr, "No directory, logging in with HOME=/\n");
 194     }
 195   }
 196
 197   /* --- Finally, sort the argument list --- */
 198
 199   {
 200     char *p, *q;
 201     int i;
 202
 203     av = xmalloc((argc + 1) * sizeof(char *));
 204     p = pw->pw_shell;
 205     for (q = p; *q; q++) {
 206       if (*q == '/')
 207         p = q + 1;
 208     }
 209     if (argv[0][0] == '-') {
 210       q = xmalloc(2 + strlen(p));
 211       *q = '-';
 212       strcpy(q + 1, p);
 213       av[0] = q;
 214     } else
 215       av[0] = p;
 216
 217     for (i = 1; i <= argc; i++)
 218       av[i] = argv[i];
 219   }
 220
 221   /* --- Run the real shell --- */
 222
 223   syslog(LOG_INFO, "chroot user `%s' logged in ok", myname);
 224   closelog();
 225   execve(pw->pw_shell, av, env);
 226   fprintf(stderr, "%s: couldn't exec `%s': %s\n",
 227           quis, pw->pw_shell, strerror(errno));
 228   return (EXIT_FAILURE);
 229 }
 230
 231 /*----- That's all, folks -------------------------------------------------*/