Need help improving a small C program [closed]

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I wanted to launch a bash script (read: bash not sh script) as a root not as the user calling it, however bash ignore setuid on scripts, so I chose to write a very small script that takes a script/arguments and call it with setuid set.

This worked well and I went even further to verify that the script has setuid set on, executable and setuid() called on the owner of the file and not as root, to avoid any misuse of the program and I ended up with the program below..

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(int argc, char **argv)
{
  char *command;
  int i, file_owner, size = 0;
  struct stat status_buf;
  ushort file_mode;

  // Check argc
  if (argc < 2) {
    printf("Usage: %s <script> [arguments]\n", argv[0]);
    return 1;
  }

  // Make sure the script does exist
  if(fopen(argv[1], "r") == NULL) {
    printf("The file %s does not exist.\n", argv[1]);
    return 1;
  }

  // Get the attributes of the file
  stat(argv[1], &status_buf);

  // Get the permissions of the file
  file_mode = status_buf.st_mode;

  // Make sure it's executable and it's setuid
  if(file_mode >> 6 != 567) {
    printf("The file %s should be executable and should have setuid set, please chmod it 开发者_如何转开发0106755.\n", argv[1]);
    return 1;
  }

  // Get the owner of the script
  file_owner = status_buf.st_uid;

  // setuid
  setuid(file_owner);

  // Generate the command
  for (i = 1; i < argc; i++) {
    size += strlen(argv[i]);
  }
  command = (char *) malloc( (size + argc + 11) * sizeof(char) );
  sprintf(command, "/bin/bash %s", argv[1]);
  if (argc > 2) {
    for (i = 2; i < argc; i++) {
      sprintf(command, "%s %s", command, argv[i]);
    }
  }

  // Execute the command
  system(command);

  // free memory
  free(command);

  return 0;
}

The exercise was not only to solve my problem, but it was also a way to get more into C, so what do you guys suggest? Is there anything I should improve ?

Thank you..

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if(file_mode >> 6 != 567) {

Magic numbers are bad. Use the S_I* bitmasks instead.

system(command);

You're on *nix; use of fork() and exec*() will eliminate most of the acrobatics performed in the loop just before.