1/*
  2 * kmod - the kernel module loader
  3 *
  4 * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
  5 */
  6
  7#include <linux/module.h>
  8#include <linux/sched.h>
  9#include <linux/sched/task.h>
 10#include <linux/binfmts.h>
 11#include <linux/syscalls.h>
 12#include <linux/unistd.h>
 13#include <linux/kmod.h>
 14#include <linux/slab.h>
 15#include <linux/completion.h>
 16#include <linux/cred.h>
 17#include <linux/file.h>
 18#include <linux/workqueue.h>
 19#include <linux/security.h>
 20#include <linux/mount.h>
 21#include <linux/kernel.h>
 22#include <linux/init.h>
 23#include <linux/resource.h>
 24#include <linux/notifier.h>
 25#include <linux/suspend.h>
 26#include <linux/rwsem.h>
 27#include <linux/ptrace.h>
 28#include <linux/async.h>
 29#include <linux/uaccess.h>
 30
 31#include <trace/events/module.h>
 32#include "internal.h"
 33
 34/*
 35 * Assuming:
 36 *
 37 * threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
 38 *		       (u64) THREAD_SIZE * 8UL);
 39 *
 40 * If you need less than 50 threads would mean we're dealing with systems
 41 * smaller than 3200 pages. This assumes you are capable of having ~13M memory,
 42 * and this would only be an upper limit, after which the OOM killer would take
 43 * effect. Systems like these are very unlikely if modules are enabled.
 44 */
 45#define MAX_KMOD_CONCURRENT 50
 46static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
 47
 48/*
 49 * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
 50 * running at the same time without returning. When this happens we
 51 * believe you've somehow ended up with a recursive module dependency
 52 * creating a loop.
 53 *
 54 * We have no option but to fail.
 55 *
 56 * Userspace should proactively try to detect and prevent these.
 57 */
 58#define MAX_KMOD_ALL_BUSY_TIMEOUT 5
 59
 60/*
 61	modprobe_path is set via /proc/sys.
 62*/
 63char modprobe_path[KMOD_PATH_LEN] = CONFIG_MODPROBE_PATH;
 64
 65static void free_modprobe_argv(struct subprocess_info *info)
 66{
 67	kfree(info->argv[3]); /* check call_modprobe() */
 68	kfree(info->argv);
 69}
 70
 71static int call_modprobe(char *orig_module_name, int wait)
 72{
 73	struct subprocess_info *info;
 74	static char *envp[] = {
 75		"HOME=/",
 76		"TERM=linux",
 77		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
 78		NULL
 79	};
 80	char *module_name;
 81	int ret;
 82
 83	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
 84	if (!argv)
 85		goto out;
 86
 87	module_name = kstrdup(orig_module_name, GFP_KERNEL);
 88	if (!module_name)
 89		goto free_argv;
 90
 91	argv[0] = modprobe_path;
 92	argv[1] = "-q";
 93	argv[2] = "--";
 94	argv[3] = module_name;	/* check free_modprobe_argv() */
 95	argv[4] = NULL;
 96
 97	info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
 98					 NULL, free_modprobe_argv, NULL);
 99	if (!info)
100		goto free_module_name;
101
102	ret = call_usermodehelper_exec(info, wait | UMH_KILLABLE);
103	kmod_dup_request_announce(orig_module_name, ret);
104	return ret;
105
106free_module_name:
107	kfree(module_name);
108free_argv:
109	kfree(argv);
110out:
111	kmod_dup_request_announce(orig_module_name, -ENOMEM);
112	return -ENOMEM;
113}
114
115/**
116 * __request_module - try to load a kernel module
117 * @wait: wait (or not) for the operation to complete
118 * @fmt: printf style format string for the name of the module
119 * @...: arguments as specified in the format string
120 *
121 * Load a module using the user mode module loader. The function returns
122 * zero on success or a negative errno code or positive exit code from
123 * "modprobe" on failure. Note that a successful module load does not mean
124 * the module did not then unload and exit on an error of its own. Callers
125 * must check that the service they requested is now available not blindly
126 * invoke it.
127 *
128 * If module auto-loading support is disabled then this function
129 * simply returns -ENOENT.
130 */
131int __request_module(bool wait, const char *fmt, ...)
132{
133	va_list args;
134	char module_name[MODULE_NAME_LEN];
135	int ret, dup_ret;
136
137	/*
138	 * We don't allow synchronous module loading from async.  Module
139	 * init may invoke async_synchronize_full() which will end up
140	 * waiting for this task which already is waiting for the module
141	 * loading to complete, leading to a deadlock.
142	 */
143	WARN_ON_ONCE(wait && current_is_async());
144
145	if (!modprobe_path[0])
146		return -ENOENT;
147
148	va_start(args, fmt);
149	ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
150	va_end(args);
151	if (ret >= MODULE_NAME_LEN)
152		return -ENAMETOOLONG;
153
154	ret = security_kernel_module_request(module_name);
155	if (ret)
156		return ret;
157
158	ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
159	if (ret) {
160		pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
161				    module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
162		return ret;
163	}
164
165	trace_module_request(module_name, wait, _RET_IP_);
166
167	if (kmod_dup_request_exists_wait(module_name, wait, &dup_ret)) {
168		ret = dup_ret;
169		goto out;
170	}
171
172	ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
173
174out:
175	up(&kmod_concurrent_max);
176
177	return ret;
178}
179EXPORT_SYMBOL(__request_module);