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(objp: info->argv[3]); /* check call_modprobe() */
68 kfree(objp: 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(s: 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(path: modprobe_path, argv, envp, GFP_KERNEL,
98 NULL, cleanup: free_modprobe_argv, NULL);
99 if (!info)
100 goto free_module_name;
101
102 ret = call_usermodehelper_exec(info, wait: wait | UMH_KILLABLE);
103 kmod_dup_request_announce(module_name: orig_module_name, ret);
104 return ret;
105
106free_module_name:
107 kfree(objp: module_name);
108free_argv:
109 kfree(objp: argv);
110out:
111 kmod_dup_request_announce(module_name: orig_module_name, ret: -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(buf: 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(kmod_name: module_name);
155 if (ret)
156 return ret;
157
158 ret = down_timeout(sem: &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(name: module_name, wait, _RET_IP_);
166
167 if (kmod_dup_request_exists_wait(module_name, wait, dup_ret: &dup_ret)) {
168 ret = dup_ret;
169 goto out;
170 }
171
172 ret = call_modprobe(orig_module_name: module_name, wait: wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
173
174out:
175 up(sem: &kmod_concurrent_max);
176
177 return ret;
178}
179EXPORT_SYMBOL(__request_module);
180

source code of linux/kernel/module/kmod.c

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