/*

   * kmod - the kernel module loader
   */

  #include <linux/module.h>
  #include <linux/sched.h>

  #include <linux/sched/task.h>

  #include <linux/binfmts.h>

  #include <linux/syscalls.h>
  #include <linux/unistd.h>
  #include <linux/kmod.h>

  #include <linux/slab.h>

  #include <linux/completion.h>

  #include <linux/cred.h>

  #include <linux/file.h>

  #include <linux/fdtable.h>

  #include <linux/workqueue.h>
  #include <linux/security.h>
  #include <linux/mount.h>
  #include <linux/kernel.h>
  #include <linux/init.h>

  #include <linux/resource.h>

  #include <linux/notifier.h>
  #include <linux/suspend.h>

  #include <linux/rwsem.h>

  #include <linux/ptrace.h>

  #include <linux/async.h>

  #include <linux/uaccess.h>

  #include <trace/events/module.h>

  /*
   * Assuming:
   *
   * threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
   *		       (u64) THREAD_SIZE * 8UL);
   *
   * If you need less than 50 threads would mean we're dealing with systems

   * smaller than 3200 pages. This assumes you are capable of having ~13M memory,

   * and this would only be an upper limit, after which the OOM killer would take
   * effect. Systems like these are very unlikely if modules are enabled.

   */
  #define MAX_KMOD_CONCURRENT 50
  static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);

  static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);

  
  /*

   * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
   * running at the same time without returning. When this happens we
   * believe you've somehow ended up with a recursive module dependency
   * creating a loop.
   *
   * We have no option but to fail.
   *
   * Userspace should proactively try to detect and prevent these.
   */
  #define MAX_KMOD_ALL_BUSY_TIMEOUT 5
  
  /*

  	modprobe_path is set via /proc/sys.
  */
  char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";

  static void free_modprobe_argv(struct subprocess_info *info)
  {
  	kfree(info->argv[3]); /* check call_modprobe() */
  	kfree(info->argv);
  }

  static int call_modprobe(char *module_name, int wait)
  {

  	struct subprocess_info *info;

  	static char *envp[] = {
  		"HOME=/",
  		"TERM=linux",
  		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  		NULL
  	};

  	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
  	if (!argv)
  		goto out;
  
  	module_name = kstrdup(module_name, GFP_KERNEL);
  	if (!module_name)
  		goto free_argv;
  
  	argv[0] = modprobe_path;
  	argv[1] = "-q";
  	argv[2] = "--";
  	argv[3] = module_name;	/* check free_modprobe_argv() */
  	argv[4] = NULL;

  	info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
  					 NULL, free_modprobe_argv, NULL);
  	if (!info)
  		goto free_module_name;
  
  	return call_usermodehelper_exec(info, wait | UMH_KILLABLE);
  
  free_module_name:
  	kfree(module_name);

  free_argv:
  	kfree(argv);
  out:
  	return -ENOMEM;

  }

  /**

   * __request_module - try to load a kernel module
   * @wait: wait (or not) for the operation to complete

   * @fmt: printf style format string for the name of the module
   * @...: arguments as specified in the format string

   *
   * Load a module using the user mode module loader. The function returns

   * zero on success or a negative errno code or positive exit code from
   * "modprobe" on failure. Note that a successful module load does not mean
   * the module did not then unload and exit on an error of its own. Callers
   * must check that the service they requested is now available not blindly
   * invoke it.

   *
   * If module auto-loading support is disabled then this function

   * simply returns -ENOENT.

   */

  int __request_module(bool wait, const char *fmt, ...)

  {
  	va_list args;
  	char module_name[MODULE_NAME_LEN];

  	int ret;

  	/*
  	 * We don't allow synchronous module loading from async.  Module
  	 * init may invoke async_synchronize_full() which will end up
  	 * waiting for this task which already is waiting for the module
  	 * loading to complete, leading to a deadlock.
  	 */
  	WARN_ON_ONCE(wait && current_is_async());

  	if (!modprobe_path[0])

  		return -ENOENT;

  	va_start(args, fmt);
  	ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  	va_end(args);
  	if (ret >= MODULE_NAME_LEN)
  		return -ENAMETOOLONG;

  	ret = security_kernel_module_request(module_name);
  	if (ret)
  		return ret;

  	if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {

  		pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
  				    atomic_read(&kmod_concurrent_max),
  				    MAX_KMOD_CONCURRENT, module_name);

  		ret = wait_event_killable_timeout(kmod_wq,
  						  atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
  						  MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
  		if (!ret) {
  			pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
  					    module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
  			return -ETIME;
  		} else if (ret == -ERESTARTSYS) {
  			pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
  			return ret;
  		}

  	}

  	trace_module_request(module_name, wait, _RET_IP_);

  	ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);

  	atomic_inc(&kmod_concurrent_max);

  	wake_up(&kmod_wq);

  	return ret;
  }

  EXPORT_SYMBOL(__request_module);