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/fdtable.h>
 19#include <linux/workqueue.h>
 20#include <linux/security.h>
 21#include <linux/mount.h>
 22#include <linux/kernel.h>
 23#include <linux/init.h>
 24#include <linux/resource.h>
 25#include <linux/notifier.h>
 26#include <linux/suspend.h>
 27#include <linux/rwsem.h>
 28#include <linux/ptrace.h>
 29#include <linux/async.h>
 30#include <linux/uaccess.h>
 31
 32#include <trace/events/module.h>
 33#include "internal.h"
 34
 35/*
 36 * Assuming:
 37 *
 38 * threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
 39 *		       (u64) THREAD_SIZE * 8UL);
 40 *
 41 * If you need less than 50 threads would mean we're dealing with systems
 42 * smaller than 3200 pages. This assumes you are capable of having ~13M memory,
 43 * and this would only be an upper limit, after which the OOM killer would take
 44 * effect. Systems like these are very unlikely if modules are enabled.
 45 */
 46#define MAX_KMOD_CONCURRENT 50
 47static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
 48
 49/*
 50 * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
 51 * running at the same time without returning. When this happens we
 52 * believe you've somehow ended up with a recursive module dependency
 53 * creating a loop.
 54 *
 55 * We have no option but to fail.
 56 *
 57 * Userspace should proactively try to detect and prevent these.
 58 */
 59#define MAX_KMOD_ALL_BUSY_TIMEOUT 5
 60
 61/*
 62	modprobe_path is set via /proc/sys.
 63*/
 64char modprobe_path[KMOD_PATH_LEN] = CONFIG_MODPROBE_PATH;
 65
 66static void free_modprobe_argv(struct subprocess_info *info)
 67{
 68	kfree(info->argv[3]); /* check call_modprobe() */
 69	kfree(info->argv);
 70}
 71
 72static int call_modprobe(char *orig_module_name, int wait)
 73{
 74	struct subprocess_info *info;
 75	static char *envp[] = {
 76		"HOME=/",
 77		"TERM=linux",
 78		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
 79		NULL
 80	};
 81	char *module_name;
 82	int ret;
 83
 84	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
 85	if (!argv)
 86		goto out;
 87
 88	module_name = kstrdup(orig_module_name, GFP_KERNEL);
 89	if (!module_name)
 90		goto free_argv;
 91
 92	argv[0] = modprobe_path;
 93	argv[1] = "-q";
 94	argv[2] = "--";
 95	argv[3] = module_name;	/* check free_modprobe_argv() */
 96	argv[4] = NULL;
 97
 98	info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
 99					 NULL, free_modprobe_argv, NULL);
100	if (!info)
101		goto free_module_name;
102
103	ret = call_usermodehelper_exec(info, wait | UMH_KILLABLE);
104	kmod_dup_request_announce(orig_module_name, ret);
105	return ret;
106
107free_module_name:
108	kfree(module_name);
109free_argv:
110	kfree(argv);
111out:
112	kmod_dup_request_announce(orig_module_name, -ENOMEM);
113	return -ENOMEM;
114}
115
116/**
117 * __request_module - try to load a kernel module
118 * @wait: wait (or not) for the operation to complete
119 * @fmt: printf style format string for the name of the module
120 * @...: arguments as specified in the format string
121 *
122 * Load a module using the user mode module loader. The function returns
123 * zero on success or a negative errno code or positive exit code from
124 * "modprobe" on failure. Note that a successful module load does not mean
125 * the module did not then unload and exit on an error of its own. Callers
126 * must check that the service they requested is now available not blindly
127 * invoke it.
128 *
129 * If module auto-loading support is disabled then this function
130 * simply returns -ENOENT.
131 */
132int __request_module(bool wait, const char *fmt, ...)
133{
134	va_list args;
135	char module_name[MODULE_NAME_LEN];
136	int ret, dup_ret;
137
138	/*
139	 * We don't allow synchronous module loading from async.  Module
140	 * init may invoke async_synchronize_full() which will end up
141	 * waiting for this task which already is waiting for the module
142	 * loading to complete, leading to a deadlock.
143	 */
144	WARN_ON_ONCE(wait && current_is_async());
145
146	if (!modprobe_path[0])
147		return -ENOENT;
148
149	va_start(args, fmt);
150	ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
151	va_end(args);
152	if (ret >= MODULE_NAME_LEN)
153		return -ENAMETOOLONG;
154
155	ret = security_kernel_module_request(module_name);
156	if (ret)
157		return ret;
158
159	ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
160	if (ret) {
161		pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
162				    module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
163		return ret;
164	}
165
166	trace_module_request(module_name, wait, _RET_IP_);
167
168	if (kmod_dup_request_exists_wait(module_name, wait, &dup_ret)) {
169		ret = dup_ret;
170		goto out;
171	}
172
173	ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
174
175out:
176	up(&kmod_concurrent_max);
177
178	return ret;
179}
180EXPORT_SYMBOL(__request_module);