Root/kernel/kmod.c

1/*
2    kmod, the new module loader (replaces kerneld)
3    Kirk Petersen
4
5    Reorganized not to be a daemon by Adam Richter, with guidance
6    from Greg Zornetzer.
7
8    Modified to avoid chroot and file sharing problems.
9    Mikael Pettersson
10
11    Limit the concurrent number of kmod modprobes to catch loops from
12    "modprobe needs a service that is in a module".
13    Keith Owens <kaos@ocs.com.au> December 1999
14
15    Unblock all signals when we exec a usermode process.
16    Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
17
18    call_usermodehelper wait flag, and remove exec_usermodehelper.
19    Rusty Russell <rusty@rustcorp.com.au> Jan 2003
20*/
21#include <linux/module.h>
22#include <linux/sched.h>
23#include <linux/syscalls.h>
24#include <linux/unistd.h>
25#include <linux/kmod.h>
26#include <linux/slab.h>
27#include <linux/completion.h>
28#include <linux/file.h>
29#include <linux/fdtable.h>
30#include <linux/workqueue.h>
31#include <linux/security.h>
32#include <linux/mount.h>
33#include <linux/kernel.h>
34#include <linux/init.h>
35#include <linux/resource.h>
36#include <linux/notifier.h>
37#include <linux/suspend.h>
38#include <asm/uaccess.h>
39
40#include <trace/events/module.h>
41
42extern int max_threads;
43
44static struct workqueue_struct *khelper_wq;
45
46#ifdef CONFIG_MODULES
47
48/*
49    modprobe_path is set via /proc/sys.
50*/
51char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
52
53/**
54 * __request_module - try to load a kernel module
55 * @wait: wait (or not) for the operation to complete
56 * @fmt: printf style format string for the name of the module
57 * @...: arguments as specified in the format string
58 *
59 * Load a module using the user mode module loader. The function returns
60 * zero on success or a negative errno code on failure. Note that a
61 * successful module load does not mean the module did not then unload
62 * and exit on an error of its own. Callers must check that the service
63 * they requested is now available not blindly invoke it.
64 *
65 * If module auto-loading support is disabled then this function
66 * becomes a no-operation.
67 */
68int __request_module(bool wait, const char *fmt, ...)
69{
70    va_list args;
71    char module_name[MODULE_NAME_LEN];
72    unsigned int max_modprobes;
73    int ret;
74    char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
75    static char *envp[] = { "HOME=/",
76                "TERM=linux",
77                "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
78                NULL };
79    static atomic_t kmod_concurrent = ATOMIC_INIT(0);
80#define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */
81    static int kmod_loop_msg;
82
83    va_start(args, fmt);
84    ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
85    va_end(args);
86    if (ret >= MODULE_NAME_LEN)
87        return -ENAMETOOLONG;
88
89    ret = security_kernel_module_request(module_name);
90    if (ret)
91        return ret;
92
93    /* If modprobe needs a service that is in a module, we get a recursive
94     * loop. Limit the number of running kmod threads to max_threads/2 or
95     * MAX_KMOD_CONCURRENT, whichever is the smaller. A cleaner method
96     * would be to run the parents of this process, counting how many times
97     * kmod was invoked. That would mean accessing the internals of the
98     * process tables to get the command line, proc_pid_cmdline is static
99     * and it is not worth changing the proc code just to handle this case.
100     * KAO.
101     *
102     * "trace the ppid" is simple, but will fail if someone's
103     * parent exits. I think this is as good as it gets. --RR
104     */
105    max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
106    atomic_inc(&kmod_concurrent);
107    if (atomic_read(&kmod_concurrent) > max_modprobes) {
108        /* We may be blaming an innocent here, but unlikely */
109        if (kmod_loop_msg++ < 5)
110            printk(KERN_ERR
111                   "request_module: runaway loop modprobe %s\n",
112                   module_name);
113        atomic_dec(&kmod_concurrent);
114        return -ENOMEM;
115    }
116
117    trace_module_request(module_name, wait, _RET_IP_);
118
119    ret = call_usermodehelper_fns(modprobe_path, argv, envp,
120            wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC,
121            NULL, NULL, NULL);
122
123    atomic_dec(&kmod_concurrent);
124    return ret;
125}
126EXPORT_SYMBOL(__request_module);
127#endif /* CONFIG_MODULES */
128
129/*
130 * This is the task which runs the usermode application
131 */
132static int ____call_usermodehelper(void *data)
133{
134    struct subprocess_info *sub_info = data;
135    int retval;
136
137    spin_lock_irq(&current->sighand->siglock);
138    flush_signal_handlers(current, 1);
139    spin_unlock_irq(&current->sighand->siglock);
140
141    /* We can run anywhere, unlike our parent keventd(). */
142    set_cpus_allowed_ptr(current, cpu_all_mask);
143
144    /*
145     * Our parent is keventd, which runs with elevated scheduling priority.
146     * Avoid propagating that into the userspace child.
147     */
148    set_user_nice(current, 0);
149
150    if (sub_info->init) {
151        retval = sub_info->init(sub_info);
152        if (retval)
153            goto fail;
154    }
155
156    retval = kernel_execve(sub_info->path,
157                   (const char *const *)sub_info->argv,
158                   (const char *const *)sub_info->envp);
159
160    /* Exec failed? */
161fail:
162    sub_info->retval = retval;
163    do_exit(0);
164}
165
166void call_usermodehelper_freeinfo(struct subprocess_info *info)
167{
168    if (info->cleanup)
169        (*info->cleanup)(info);
170    kfree(info);
171}
172EXPORT_SYMBOL(call_usermodehelper_freeinfo);
173
174/* Keventd can't block, but this (a child) can. */
175static int wait_for_helper(void *data)
176{
177    struct subprocess_info *sub_info = data;
178    pid_t pid;
179
180    /* If SIGCLD is ignored sys_wait4 won't populate the status. */
181    spin_lock_irq(&current->sighand->siglock);
182    current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
183    spin_unlock_irq(&current->sighand->siglock);
184
185    pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
186    if (pid < 0) {
187        sub_info->retval = pid;
188    } else {
189        int ret = -ECHILD;
190        /*
191         * Normally it is bogus to call wait4() from in-kernel because
192         * wait4() wants to write the exit code to a userspace address.
193         * But wait_for_helper() always runs as keventd, and put_user()
194         * to a kernel address works OK for kernel threads, due to their
195         * having an mm_segment_t which spans the entire address space.
196         *
197         * Thus the __user pointer cast is valid here.
198         */
199        sys_wait4(pid, (int __user *)&ret, 0, NULL);
200
201        /*
202         * If ret is 0, either ____call_usermodehelper failed and the
203         * real error code is already in sub_info->retval or
204         * sub_info->retval is 0 anyway, so don't mess with it then.
205         */
206        if (ret)
207            sub_info->retval = ret;
208    }
209
210    complete(sub_info->complete);
211    return 0;
212}
213
214/* This is run by khelper thread */
215static void __call_usermodehelper(struct work_struct *work)
216{
217    struct subprocess_info *sub_info =
218        container_of(work, struct subprocess_info, work);
219    enum umh_wait wait = sub_info->wait;
220    pid_t pid;
221
222    /* CLONE_VFORK: wait until the usermode helper has execve'd
223     * successfully We need the data structures to stay around
224     * until that is done. */
225    if (wait == UMH_WAIT_PROC)
226        pid = kernel_thread(wait_for_helper, sub_info,
227                    CLONE_FS | CLONE_FILES | SIGCHLD);
228    else
229        pid = kernel_thread(____call_usermodehelper, sub_info,
230                    CLONE_VFORK | SIGCHLD);
231
232    switch (wait) {
233    case UMH_NO_WAIT:
234        call_usermodehelper_freeinfo(sub_info);
235        break;
236
237    case UMH_WAIT_PROC:
238        if (pid > 0)
239            break;
240        /* FALLTHROUGH */
241    case UMH_WAIT_EXEC:
242        if (pid < 0)
243            sub_info->retval = pid;
244        complete(sub_info->complete);
245    }
246}
247
248#ifdef CONFIG_PM_SLEEP
249/*
250 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
251 * (used for preventing user land processes from being created after the user
252 * land has been frozen during a system-wide hibernation or suspend operation).
253 */
254static int usermodehelper_disabled;
255
256/* Number of helpers running */
257static atomic_t running_helpers = ATOMIC_INIT(0);
258
259/*
260 * Wait queue head used by usermodehelper_pm_callback() to wait for all running
261 * helpers to finish.
262 */
263static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
264
265/*
266 * Time to wait for running_helpers to become zero before the setting of
267 * usermodehelper_disabled in usermodehelper_pm_callback() fails
268 */
269#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
270
271/**
272 * usermodehelper_disable - prevent new helpers from being started
273 */
274int usermodehelper_disable(void)
275{
276    long retval;
277
278    usermodehelper_disabled = 1;
279    smp_mb();
280    /*
281     * From now on call_usermodehelper_exec() won't start any new
282     * helpers, so it is sufficient if running_helpers turns out to
283     * be zero at one point (it may be increased later, but that
284     * doesn't matter).
285     */
286    retval = wait_event_timeout(running_helpers_waitq,
287                    atomic_read(&running_helpers) == 0,
288                    RUNNING_HELPERS_TIMEOUT);
289    if (retval)
290        return 0;
291
292    usermodehelper_disabled = 0;
293    return -EAGAIN;
294}
295
296/**
297 * usermodehelper_enable - allow new helpers to be started again
298 */
299void usermodehelper_enable(void)
300{
301    usermodehelper_disabled = 0;
302}
303
304static void helper_lock(void)
305{
306    atomic_inc(&running_helpers);
307    smp_mb__after_atomic_inc();
308}
309
310static void helper_unlock(void)
311{
312    if (atomic_dec_and_test(&running_helpers))
313        wake_up(&running_helpers_waitq);
314}
315#else /* CONFIG_PM_SLEEP */
316#define usermodehelper_disabled 0
317
318static inline void helper_lock(void) {}
319static inline void helper_unlock(void) {}
320#endif /* CONFIG_PM_SLEEP */
321
322/**
323 * call_usermodehelper_setup - prepare to call a usermode helper
324 * @path: path to usermode executable
325 * @argv: arg vector for process
326 * @envp: environment for process
327 * @gfp_mask: gfp mask for memory allocation
328 *
329 * Returns either %NULL on allocation failure, or a subprocess_info
330 * structure. This should be passed to call_usermodehelper_exec to
331 * exec the process and free the structure.
332 */
333struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
334                          char **envp, gfp_t gfp_mask)
335{
336    struct subprocess_info *sub_info;
337    sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
338    if (!sub_info)
339        goto out;
340
341    INIT_WORK(&sub_info->work, __call_usermodehelper);
342    sub_info->path = path;
343    sub_info->argv = argv;
344    sub_info->envp = envp;
345  out:
346    return sub_info;
347}
348EXPORT_SYMBOL(call_usermodehelper_setup);
349
350/**
351 * call_usermodehelper_setfns - set a cleanup/init function
352 * @info: a subprocess_info returned by call_usermodehelper_setup
353 * @cleanup: a cleanup function
354 * @init: an init function
355 * @data: arbitrary context sensitive data
356 *
357 * The init function is used to customize the helper process prior to
358 * exec. A non-zero return code causes the process to error out, exit,
359 * and return the failure to the calling process
360 *
361 * The cleanup function is just before ethe subprocess_info is about to
362 * be freed. This can be used for freeing the argv and envp. The
363 * Function must be runnable in either a process context or the
364 * context in which call_usermodehelper_exec is called.
365 */
366void call_usermodehelper_setfns(struct subprocess_info *info,
367            int (*init)(struct subprocess_info *info),
368            void (*cleanup)(struct subprocess_info *info),
369            void *data)
370{
371    info->cleanup = cleanup;
372    info->init = init;
373    info->data = data;
374}
375EXPORT_SYMBOL(call_usermodehelper_setfns);
376
377/**
378 * call_usermodehelper_exec - start a usermode application
379 * @sub_info: information about the subprocessa
380 * @wait: wait for the application to finish and return status.
381 * when -1 don't wait at all, but you get no useful error back when
382 * the program couldn't be exec'ed. This makes it safe to call
383 * from interrupt context.
384 *
385 * Runs a user-space application. The application is started
386 * asynchronously if wait is not set, and runs as a child of keventd.
387 * (ie. it runs with full root capabilities).
388 */
389int call_usermodehelper_exec(struct subprocess_info *sub_info,
390                 enum umh_wait wait)
391{
392    DECLARE_COMPLETION_ONSTACK(done);
393    int retval = 0;
394
395    helper_lock();
396    if (sub_info->path[0] == '\0')
397        goto out;
398
399    if (!khelper_wq || usermodehelper_disabled) {
400        retval = -EBUSY;
401        goto out;
402    }
403
404    sub_info->complete = &done;
405    sub_info->wait = wait;
406
407    queue_work(khelper_wq, &sub_info->work);
408    if (wait == UMH_NO_WAIT) /* task has freed sub_info */
409        goto unlock;
410    wait_for_completion(&done);
411    retval = sub_info->retval;
412
413out:
414    call_usermodehelper_freeinfo(sub_info);
415unlock:
416    helper_unlock();
417    return retval;
418}
419EXPORT_SYMBOL(call_usermodehelper_exec);
420
421void __init usermodehelper_init(void)
422{
423    khelper_wq = create_singlethread_workqueue("khelper");
424    BUG_ON(!khelper_wq);
425}
426

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