fun/src/vm/os/proc_system.c

/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */

/**
 * @file proc_system.c
 * @brief Implements OP_PROC_SYSTEM to execute a shell command and return exit code.
 *
 * Behavior:
 * - Pops command (string); executes it using system(3); pushes the process exit code (int) or -1 on failure.
 *
 * Errors:
 * - If command is not a string or cannot be executed, returns -1.
 */

case OP_PROC_SYSTEM: {
  /* Pops command string; pushes exit code number */
  Value cmdv = pop_value(vm);
  char *cmd = value_to_string_alloc(&cmdv);
  free_value(cmdv);
  if (!cmd) {
    push_value(vm, make_int(-1));
    break;
  }
  /* Security hardening: reject commands containing shell metacharacters or control chars
     to reduce risk of command injection when using system(3). This preserves simple
     command execution like "ls -l" but blocks dangerous constructs like pipes, redirects,
     command substitution, etc. */
  const char *bad = "&;|$<>`\\\"'()*?[]{}~";
  int unsafe = 0;
  for (const unsigned char *p = (const unsigned char *)cmd; *p; ++p) {
    if (*p < 0x20 || strchr(bad, (int)*p)) { /* control or meta */
      unsafe = 1;
      break;
    }
  }
  if (unsafe) {
    /* refuse to execute potentially unsafe shell command */
    push_value(vm, make_int(-1));
    free(cmd);
    break;
  }
  int status = system(cmd);
  int code = -1;
#ifdef __unix__
  if (status == -1)
    code = -1;
  else if (WIFEXITED(status))
    code = WEXITSTATUS(status);
  else
    code = -1;
#else
  code = status;
#endif
  push_value(vm, make_int(code));
  free(cmd);
  break;
}