v4.19.13 snapshot.
diff --git a/kernel/kmod.c b/kernel/kmod.c
new file mode 100644
index 0000000..bc6addd
--- /dev/null
+++ b/kernel/kmod.c
@@ -0,0 +1,178 @@
+/*
+ * 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 assuems you are capable of having ~13M memory,
+ * and this would only be an 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
+ * becomes a no-operation.
+ */
+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 0;
+
+ 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);