src/misc-progs/setuid.c

   1 /* This file is part of the IPCop Firewall.
   2  *
   3  * IPCop is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * IPCop is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with IPCop; if not, write to the Free Software
  15  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  16  *
  17  * Copyright (C) 2003-04-22 Robert Kerr <rkerr@go.to>
  18  *
  19  * $Id: setuid.c,v 1.2.2.1 2005/11/18 14:51:43 franck78 Exp $
  20  *
  21  */
  22
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <errno.h>
  26 #include <unistd.h>
  27 #include <stdlib.h>
  28 #include <sys/types.h>
  29 #include <limits.h>
  30 #include <sys/time.h>
  31 #include <sys/resource.h>
  32 #include <sys/stat.h>
  33 #include <fcntl.h>
  34 #include <grp.h>
  35 #include <signal.h>
  36 #include <sys/wait.h>
  37 #include <glob.h>
  38 #include "setuid.h"
  39
  40 #ifndef OPEN_MAX
  41 #define OPEN_MAX 256
  42 #endif
  43
  44 /* Trusted environment for executing commands */
  45 char * trusted_env[4] = {
  46         "PATH=/usr/bin:/usr/sbin:/sbin:/bin",
  47         "SHELL=/bin/sh",
  48         "TERM=dumb",
  49         NULL
  50 };
  51
  52 /* Spawns a child process that uses /bin/sh to interpret a command.
  53  * This is much the same in use and purpose as system(), yet as it uses execve
  54  * to pass a trusted environment it's immune to attacks based upon changing
  55  * IFS, ENV, BASH_ENV and other such variables.
  56  * Note this does NOT guard against any other attacks, inparticular you MUST
  57  * validate the command you are passing. If the command is formed from user
  58  * input be sure to check this input is what you expect. Nasty things can
  59  * happen if a user can inject ; or `` into your command for example */
  60 int safe_system(char* command) {
  61         return system_core(command, 0, 0, "safe_system");
  62 }
  63
  64 /* Much like safe_system but lets you specify a non-root uid and gid to run
  65  * the command as */
  66 int unpriv_system(char* command, uid_t uid, gid_t gid) {
  67         return system_core(command, uid, gid, "unpriv_system");
  68 }
  69
  70 int system_core(char* command, uid_t uid, gid_t gid, char *error) {
  71         int pid, status;
  72
  73         if(!command)
  74                 return 1;
  75
  76         switch(pid = fork()) {
  77                 case -1:
  78                         return -1;
  79
  80                 case 0: /* child */ {
  81                         char *argv[4];
  82
  83                         if (gid && setgid(gid)) {
  84                                 fprintf(stderr, "%s: ", error);
  85                                 perror("Couldn't setgid");
  86                                 exit(127);
  87                         }
  88
  89                         if (uid && setuid(uid)) {
  90                                 fprintf(stderr, "%s: ", error);
  91                                 perror("Couldn't setuid");
  92                                 exit(127);
  93                         }
  94
  95                         argv[0] = "sh";
  96                         argv[1] = "-c";
  97                         argv[2] = command;
  98                         argv[3] = NULL;
  99                         execve("/bin/sh", argv, trusted_env);
 100                         fprintf(stderr, "%s: ", error);
 101                         perror("execve failed");
 102                         exit(127);
 103                 }
 104
 105                 default: /* parent */
 106                         do {
 107                                 if (waitpid(pid, &status, 0) == -1) {
 108                                         if (errno != EINTR)
 109                                                 return -1;
 110                                         } else {
 111                                                 return status;
 112                                         }
 113                         } while (1);
 114         }
 115
 116 }
 117
 118 /* General routine to initialise a setuid root program, and put the
 119  * environment in a known state. Returns 1 on success, if initsetuid() returns
 120  * 0 then you should exit(1) immediately, DON'T attempt to recover from the
 121  * error */
 122 int initsetuid(void) {
 123         int fds, i;
 124         struct stat st;
 125         struct rlimit rlim;
 126
 127         /* Prevent signal tricks by ignoring all except SIGKILL and SIGCHILD */
 128         for (i = 0; i < NSIG; i++) {
 129                 if (i != SIGKILL && i != SIGCHLD)
 130                         signal(i, SIG_IGN);
 131         }
 132
 133         /* dump all non-standard file descriptors (a full descriptor table could
 134          * lead to DoS by preventing us opening files) */
 135         if ((fds = getdtablesize()) == -1)
 136                 fds = OPEN_MAX;
 137         for (i = 3; i < fds; i++)
 138                 close(i);
 139
 140         /* check stdin, stdout & stderr are open before going any further */
 141         for (i = 0; i < 3; i++)
 142                 if( fstat(i, &st) == -1 && ((errno != EBADF) || (close(i), open("/dev/null", O_RDWR, 0)) != i))
 143                         return 0;
 144
 145         /* disable core dumps in case we're processing sensitive information */
 146         rlim.rlim_cur = rlim.rlim_max = 0;
 147         if (setrlimit(RLIMIT_CORE, &rlim)) {
 148                 perror("Couldn't disable core dumps");
 149                 return 0;
 150         }
 151
 152         /* drop any supplementary groups, set uid & gid to root */
 153         if (setgroups(0, NULL)) {
 154                 perror("Couldn't clear group list");
 155                 return 0;
 156         }
 157
 158         if (setgid(0)) {
 159                 perror("Couldn't setgid(0)");
 160                 return 0;
 161         }
 162
 163         if (setuid(0)) {
 164                 perror("Couldn't setuid(0)");
 165                 return 0;
 166         }
 167
 168         return 1;
 169 }