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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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