/*
 * =====================================================================================
 *
 *       Filename:  app.c
 *
 *    Description: playing with finding writable files or directories on the host
 *
 *        Version:  1.0
 *        Created:  10/20/2023 06:41:29 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Vincent Batts <vbatts@hashbangbash.com>
 *
 * =====================================================================================
 */

#define _XOPEN_SOURCE 500
#include <ftw.h>

#include <linux/limits.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <limits.h>

uid_t uid;
gid_t gid;
int ngroups;
gid_t groups[NGROUPS_MAX];

int
check_dir(const char *fpath, const struct stat *sb,
          int typeflag, struct FTW *ftwbuf) {
  int finding = 0;

  if (sb->st_uid != uid && sb->st_mode & S_IWOTH)
    finding |= 1;
  if (sb->st_uid != uid && sb->st_gid == gid && sb->st_mode & S_IWGRP)
    finding |= 2;

  for (int i = 0; i < ngroups; i++) {
    if (sb->st_uid != uid && sb->st_gid == groups[i] && sb->st_mode & S_IWGRP)
      finding |= 4;
  }

  if (typeflag == FTW_SLN || typeflag == FTW_SL)
    return 0;

  if (finding != 0) {
    printf("--> %s (m: %jo; t: %s; uid: %d; gid: %d)\n", fpath,
           (uintmax_t) sb->st_mode,
           (typeflag == FTW_D) ? "d" : (typeflag == FTW_F) ? "f" :
           (typeflag == FTW_SL) ? "sl" : (typeflag == FTW_SLN) ? "sln" : "???",
           sb->st_uid,
           sb->st_gid);
    if (finding&1)
      printf("  owned by another user and is world writable\n");
    if (finding&2)
      printf("  owned by another user and is group writable by our group\n");
    if (finding&4)
      printf("  owned by another user and is group writable by a group we are a member of\n");
  }
  return EXIT_SUCCESS;
}

int
main(int argc, char** argv) {
  uid = geteuid();
  gid = getegid();
  ngroups = getgroups(NGROUPS_MAX, groups);

  int flags = 0;
  flags |= FTW_PHYS; // don't follow symlinks

  for (int i = 1; i < argc; i++) {
    printf("arg[%d] %s\n", i, argv[i]);

    int ret;
    ret = nftw(argv[i], &check_dir, 1024, flags);
    if (ret != EXIT_SUCCESS) {
      printf("FAILURE walking %s\n", argv[i]);
    }
  }

	return EXIT_SUCCESS;
}