xref: /linux/kernel/module/kmod.c (revision 2363088eba2ecccfb643725e4864af73c4226a04)
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
47 static 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 */
64 char modprobe_path[KMOD_PATH_LEN] = CONFIG_MODPROBE_PATH;
65 
66 static void free_modprobe_argv(struct subprocess_info *info)
67 {
68 	kfree(info->argv[3]); /* check call_modprobe() */
69 	kfree(info->argv);
70 }
71 
72 static 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 
107 free_module_name:
108 	kfree(module_name);
109 free_argv:
110 	kfree(argv);
111 out:
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  */
132 int __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 
175 out:
176 	up(&kmod_concurrent_max);
177 
178 	return ret;
179 }
180 EXPORT_SYMBOL(__request_module);
181