memrun.c

memrun.c

#define _GNU_SOURCE

#include <stdio.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdint.h>


#ifndef NDEBUG
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#else
#define DEBUG(...)
#endif

/* memrun - load executable into memory and run it
 * polprog 20.07.2023, version 1.0
 * A modification of Guilherme Thomazi's implementation
 * which runs the executable under a custom name,
 * this version runs an executable with empty name.
 */

int main(int argc, char** argv, char** envp){

  if(argc < 2) {
    fprintf(stderr, "Give executable name\n");
    return 1;
  }

  int target = open(argv[1], O_RDONLY);
  DEBUG("file open: fd:%d\n", target);
  
  struct stat file_stat;
  fstat(target, &file_stat);
  DEBUG("filesz = %d\n", file_stat.st_size);

  void* tgt = mmap(NULL, file_stat.st_size, PROT_EXEC, MAP_PRIVATE, target, 0);  
  DEBUG("target in memory=%p\n", tgt);
  
  close(target);
  DEBUG("target fd closed\n");
  
  //flags may be MFD_CLOEXEC, but it will fail on scripts.
  //see fexecve man page part on ENOENT errno.
  int memfd = memfd_create("", 0); 
  DEBUG("Memory fd = %d\n", memfd);
  write(memfd, tgt, file_stat.st_size);
  
  DEBUG("Running the memory executable...\n");
  char* argv2[] = {(char*)0};
  int rc = fexecve(memfd, argv2, envp);
  //Guilherme's version
  //int rc = execve("/proc/self/fd/3", argv2, envp);
  
  //This should never print because we execve
  if(errno) perror("fexecve(memfd, ..)");
  DEBUG("Post fexecve, rc=%d\n", rc);
  printf("ok\n");
  
  
  return 0;

}