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:<\/p>\n
\r\n\/*\r\n * Simple su binary\r\n * Copyright (C) 2012 Compdigitec\r\n * http:\/\/www.compdigitec.com\/labs\/2012\/11\/23\/a-simple-su-implementation-in-c\/\r\n *\r\n * Redistribution and use in source and binary forms, with or without\r\n * modification, are permitted provided that the following conditions are\r\n * met:\r\n *\r\n * * Redistributions of source code must retain the above copyright\r\n * notice, this list of conditions and the following disclaimer.\r\n * * Redistributions in binary form must reproduce the above\r\n * copyright notice, this list of conditions and the following disclaimer\r\n * in the documentation and\/or other materials provided with the\r\n * distribution.\r\n * * Neither the name of Compdigitec nor the names of its\r\n * contributors may be used to endorse or promote products derived from\r\n * this software without specific prior written permission.\r\n *\r\n * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS\r\n * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT\r\n * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR\r\n * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT\r\n * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,\r\n * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT\r\n * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,\r\n * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY\r\n * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT\r\n * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE\r\n * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.\r\n *\r\n *\/\r\n\r\n#include <unistd.h>\r\n#include <getopt.h>\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <pwd.h>\r\n\r\n#define SHELL "\/system\/bin\/sh"\r\n\r\n#define about() do { \\\r\n printf("Simple crude su binary\\n"); \\\r\n printf("See http:\/\/www.compdigitec.com\/labs\/2012\/11\/23\/a-simple-su-implementation-in-c\/\\n"); \\\r\n printf("su [-c <command>] [-h] [-v] [user id to su to, must be integer]\\n"); \\\r\n } while(0)\r\n\r\nint main(int argc, char* argv[]) {\r\n char* command = NULL;\r\n int user = 0; \/\/ root\r\n int group = 0;\r\n\r\n struct option long_opts[] = {\r\n { "command",\trequired_argument,\t\tNULL, 'c' },\r\n { "help", \t\tno_argument,\t\t\tNULL, 'h' },\r\n { "shell",\t\trequired_argument,\t\tNULL, 's' },\r\n { "version",\tno_argument,\t\t\tNULL, 'v' },\r\n { NULL, 0, NULL, 0 },\r\n };\r\n\r\n int c;\r\n while((c = getopt_long(argc, argv, "+c:hsv", long_opts, NULL)) != -1) {\r\n switch(c) {\r\n case 'c':\r\n command = strdup(optarg);\r\n break;\r\n case 'h':\r\n about();\r\n exit(EXIT_SUCCESS);\r\n break;\r\n case 'v':\r\n about();\r\n exit(EXIT_SUCCESS);\r\n default:\r\n fprintf(stderr, "\\n");\r\n about();\r\n exit(EXIT_SUCCESS);\r\n }\r\n }\r\n\r\n if(command == NULL)\r\n command = strdup(SHELL);\r\n\r\n if(optind < argc) {\r\n user = atoi( argv[optind++] );\r\n }\r\n\r\n \/\/ Let's get the group ID as well.\r\n struct passwd* tempPwdPtr;\r\n#if 0\r\n struct passwd theentry;\r\n char* buf = malloc(sysconf(_SC_GETGR_R_SIZE_MAX));\r\n if(getpwuid_r(user, &theentry, buf, sysconf(_SC_GETGR_R_SIZE_MAX), &tempPwdPtr) == 0) {\r\n group = theentry.pw_gid;\r\n free(buf);\r\n }\r\n#else\r\n if((tempPwdPtr = getpwuid(user)) != NULL) {\r\n group = tempPwdPtr->pw_gid;\r\n }\r\n#endif\r\n\r\n \/\/printf("Command: %s, User to run as: %i, GID = %i\\n",command,user,group);\r\n setgid(group);\r\n setuid(user);\r\n system(command);\r\n\r\n free(command);\r\n return 0;\r\n}\r\n<\/pre>","protected":false},"excerpt":{"rendered":"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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[3],"tags":[],"_links":{"self":[{"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/posts\/326"}],"collection":[{"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/comments?post=326"}],"version-history":[{"count":0,"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/posts\/326\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/media?parent=326"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/categories?post=326"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.compdigitec.com\/labs\/wp-json\/wp\/v2\/tags?post=326"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}