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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   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 /*----- Header files ------------------------------------------------------*/
  28
  29 #include <errno.h>
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33
  34 #include <sys/types.h>
  35 #include <unistd.h>
  36 #include <syslog.h>
  37 #include <pwd.h>
  38
  39 extern char **environ;
  40
  41 /*----- Main code ---------------------------------------------------------*/
  42
  43 #ifndef CHROOTSH_PATH
  44 #  define CHROOTSH_PATH "/usr/bin/chrootsh"
  45 #endif
  46
  47 static const char *quis = "chrootsh";
  48
  49 static void *xmalloc(size_t sz)
  50 {
  51   void *p = malloc(sz);
  52   if (!p) {
  53     setuid(getuid());
  54     fprintf(stderr, "%s: not enough memory\n", quis);
  55     exit(EXIT_FAILURE);
  56   }
  57   return (p);
  58 }
  59
  60 static char *xstrdup(const char *p)
  61 {
  62   size_t sz = strlen(p) + 1;
  63   char *q = xmalloc(sz);
  64   memcpy(q, p, sz);
  65   return (q);
  66 }
  67
  68 int main(int argc, char *argv[])
  69 {
  70   struct passwd *pw;
  71   uid_t me = getuid();
  72   char *myname;
  73   char **env;
  74   char **av;
  75
  76   /* --- Resolve the program name --- */
  77
  78   {
  79     char *p, *q;
  80     p = argv[0];
  81     for (q = argv[0]; *q; q++) {
  82       if (*q == '/')
  83         p = q + 1;
  84     }
  85     if (*p == '-')
  86       p++;
  87     quis = p;
  88     openlog(quis, LOG_PID | LOG_NDELAY, LOG_DAEMON);
  89   }
  90
  91   /* --- Check the user is meant to be chrooted --- */
  92
  93   {
  94     uid_t eff = geteuid();
  95
  96     setreuid(eff, me);
  97     pw = getpwuid(me);
  98     if (!pw) {
  99       syslog(LOG_ERR, "executed by non-existant user (uid = %i)", (int)me);
 100       fprintf(stderr, "%s: you don't exist.  Go away.\n", quis);
 101       exit(EXIT_FAILURE);
 102     }
 103     if (strcmp(pw->pw_shell, CHROOTSH_PATH) != 0) {
 104       syslog(LOG_ERR, "executed by non-chrooted user `%s'", pw->pw_name);
 105       fprintf(stderr, "%s: you aren't a chrooted user\n", quis);
 106       exit(EXIT_FAILURE);
 107     }
 108     endpwent();
 109     setreuid(me, eff);
 110   }
 111
 112   /* --- Chroot the user --- */
 113
 114   {
 115     char *p = xstrdup(pw->pw_dir);
 116     char *q = strstr(p, "/./");
 117     if (q)
 118       *q = 0;
 119
 120     if (chdir(p) || chroot(p)) {
 121       int e = errno;
 122       syslog(LOG_ERR, "error entering chroot gaol: %m");
 123       setuid(me);
 124       fprintf(stderr, "%s: couldn't call chroot: %s\n", quis, strerror(e));
 125       exit(EXIT_FAILURE);
 126     }
 127     setuid(me);
 128     free(p);
 129   }
 130
 131   /* --- Read the new password block --- */
 132
 133   myname = xstrdup(pw->pw_name);
 134   pw = getpwnam(myname);
 135   if (!pw) {
 136     syslog(LOG_ERR,
 137            "configuration error: user `%s' not defined in gaol", myname);
 138     fprintf(stderr, "%s: you don't exist in the gaol\n", quis);
 139     exit(EXIT_FAILURE);
 140   }
 141   endpwent();
 142
 143   /* --- Now fiddle with environment strings and suchlike --- */
 144
 145   {
 146     size_t n;
 147     char **homevar = 0;
 148     for (n = 0; environ[n]; n++)
 149       ;
 150     env = xmalloc((n + 1) * sizeof(char *));
 151
 152     for (n = 0; environ[n]; n++) {
 153       if (strncmp(environ[n], "HOME=", 5) == 0) {
 154         char *p = xmalloc(6 + strlen(pw->pw_dir));
 155         sprintf(p, "HOME=%s", pw->pw_dir);
 156         homevar = &env[n];
 157         env[n] = p;
 158       } else if (strncmp(environ[n], "SHELL=", 6) == 0) {
 159         char *p = xmalloc(7 + strlen(pw->pw_shell));
 160         sprintf(p, "SHELL=%s", pw->pw_shell);
 161         env[n] = p;
 162       } else
 163         env[n] = environ[n];
 164     }
 165     env[n] = 0;
 166
 167     /* --- Change directory (again) --- */
 168
 169     if (chdir(pw->pw_dir)) {
 170       if (homevar) {
 171         free(*homevar);
 172         *homevar = "HOME=/";
 173       }
 174       fprintf(stderr, "No directory, logging in with HOME=/\n");
 175     }
 176   }
 177
 178   /* --- Finally, sort the argument list --- */
 179
 180   {
 181     char *p, *q;
 182     int i;
 183
 184     av = xmalloc((argc + 1) * sizeof(char *));
 185     p = pw->pw_shell;
 186     for (q = p; *q; q++) {
 187       if (*q == '/')
 188         p = q + 1;
 189     }
 190     if (argv[0][0] == '-') {
 191       q = xmalloc(2 + strlen(p));
 192       *q = '-';
 193       strcpy(q + 1, p);
 194       av[0] = q;
 195     } else
 196       av[0] = p;
 197
 198     for (i = 1; i <= argc; i++)
 199       av[i] = argv[i];
 200   }
 201
 202   /* --- Run the real shell --- */
 203
 204   syslog(LOG_INFO, "chroot user `%s' logged in ok", myname);
 205   closelog();
 206   execve(pw->pw_shell, av, env);
 207   fprintf(stderr, "%s: couldn't exec `%s': %s\n",
 208           quis, pw->pw_shell, strerror(errno));
 209   return (EXIT_FAILURE);
 210 }
 211
 212 /*----- That's all, folks -------------------------------------------------*/