/*
 * 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] = CONFIG_MODPROBE_PATH;

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);