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A simple su implementation in C
By admin | November 23, 2012
Sometimes, you might need to keep things simple. Here is a very simple su implementation written in portable C that can be used on almost any architecture – e.g. Embedded Linux, Android, Windows, etc as long as it supports C. It is licensed under the 3-clause BSD licence so any use is OK as long as credit is given:
/* * Simple su binary * Copyright (C) 2012 Compdigitec * http://www.compdigitec.com/labs/2012/11/23/a-simple-su-implementation-in-c/ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are * met: * * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above * copyright notice, this list of conditions and the following disclaimer * in the documentation and/or other materials provided with the * distribution. * * Neither the name of Compdigitec nor the names of its * contributors may be used to endorse or promote products derived from * this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * */ #include <unistd.h> #include <getopt.h> #include <stdio.h> #include <stdlib.h> #include <pwd.h> #define SHELL "/system/bin/sh" #define about() do { \ printf("Simple crude su binary\n"); \ printf("See http://www.compdigitec.com/labs/2012/11/23/a-simple-su-implementation-in-c/\n"); \ printf("su [-c <command>] [-h] [-v] [user id to su to, must be integer]\n"); \ } while(0) int main(int argc, char* argv[]) { char* command = NULL; int user = 0; // root int group = 0; struct option long_opts[] = { { "command", required_argument, NULL, 'c' }, { "help", no_argument, NULL, 'h' }, { "shell", required_argument, NULL, 's' }, { "version", no_argument, NULL, 'v' }, { NULL, 0, NULL, 0 }, }; int c; while((c = getopt_long(argc, argv, "+c:hsv", long_opts, NULL)) != -1) { switch(c) { case 'c': command = strdup(optarg); break; case 'h': about(); exit(EXIT_SUCCESS); break; case 'v': about(); exit(EXIT_SUCCESS); default: fprintf(stderr, "\n"); about(); exit(EXIT_SUCCESS); } } if(command == NULL) command = strdup(SHELL); if(optind < argc) { user = atoi( argv[optind++] ); } // Let's get the group ID as well. struct passwd* tempPwdPtr; #if 0 struct passwd theentry; char* buf = malloc(sysconf(_SC_GETGR_R_SIZE_MAX)); if(getpwuid_r(user, &theentry, buf, sysconf(_SC_GETGR_R_SIZE_MAX), &tempPwdPtr) == 0) { group = theentry.pw_gid; free(buf); } #else if((tempPwdPtr = getpwuid(user)) != NULL) { group = tempPwdPtr->pw_gid; } #endif //printf("Command: %s, User to run as: %i, GID = %i\n",command,user,group); setgid(group); setuid(user); system(command); free(command); return 0; }
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Topics: Linux | 7 Comments »
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