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(modprobe_path, argv, envp,
120            wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
121    atomic_dec(&kmod_concurrent);
122    return ret;
123}
124EXPORT_SYMBOL(__request_module);
125#endif /* CONFIG_MODULES */
126
127struct subprocess_info {
128    struct work_struct work;
129    struct completion *complete;
130    struct cred *cred;
131    char *path;
132    char **argv;
133    char **envp;
134    enum umh_wait wait;
135    int retval;
136    struct file *stdin;
137    void (*cleanup)(char **argv, char **envp);
138};
139
140/*
141 * This is the task which runs the usermode application
142 */
143static int ____call_usermodehelper(void *data)
144{
145    struct subprocess_info *sub_info = data;
146    int retval;
147
148    BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
149
150    /* Unblock all signals */
151    spin_lock_irq(&current->sighand->siglock);
152    flush_signal_handlers(current, 1);
153    sigemptyset(&current->blocked);
154    recalc_sigpending();
155    spin_unlock_irq(&current->sighand->siglock);
156
157    /* Install the credentials */
158    commit_creds(sub_info->cred);
159    sub_info->cred = NULL;
160
161    /* Install input pipe when needed */
162    if (sub_info->stdin) {
163        struct files_struct *f = current->files;
164        struct fdtable *fdt;
165        /* no races because files should be private here */
166        sys_close(0);
167        fd_install(0, sub_info->stdin);
168        spin_lock(&f->file_lock);
169        fdt = files_fdtable(f);
170        FD_SET(0, fdt->open_fds);
171        FD_CLR(0, fdt->close_on_exec);
172        spin_unlock(&f->file_lock);
173
174        /* and disallow core files too */
175        current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
176    }
177
178    /* We can run anywhere, unlike our parent keventd(). */
179    set_cpus_allowed_ptr(current, cpu_all_mask);
180
181    /*
182     * Our parent is keventd, which runs with elevated scheduling priority.
183     * Avoid propagating that into the userspace child.
184     */
185    set_user_nice(current, 0);
186
187    retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
188
189    /* Exec failed? */
190    sub_info->retval = retval;
191    do_exit(0);
192}
193
194void call_usermodehelper_freeinfo(struct subprocess_info *info)
195{
196    if (info->cleanup)
197        (*info->cleanup)(info->argv, info->envp);
198    if (info->cred)
199        put_cred(info->cred);
200    kfree(info);
201}
202EXPORT_SYMBOL(call_usermodehelper_freeinfo);
203
204/* Keventd can't block, but this (a child) can. */
205static int wait_for_helper(void *data)
206{
207    struct subprocess_info *sub_info = data;
208    pid_t pid;
209
210    /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
211     * populate the status, but will return -ECHILD. */
212    allow_signal(SIGCHLD);
213
214    pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
215    if (pid < 0) {
216        sub_info->retval = pid;
217    } else {
218        int ret;
219
220        /*
221         * Normally it is bogus to call wait4() from in-kernel because
222         * wait4() wants to write the exit code to a userspace address.
223         * But wait_for_helper() always runs as keventd, and put_user()
224         * to a kernel address works OK for kernel threads, due to their
225         * having an mm_segment_t which spans the entire address space.
226         *
227         * Thus the __user pointer cast is valid here.
228         */
229        sys_wait4(pid, (int __user *)&ret, 0, NULL);
230
231        /*
232         * If ret is 0, either ____call_usermodehelper failed and the
233         * real error code is already in sub_info->retval or
234         * sub_info->retval is 0 anyway, so don't mess with it then.
235         */
236        if (ret)
237            sub_info->retval = ret;
238    }
239
240    if (sub_info->wait == UMH_NO_WAIT)
241        call_usermodehelper_freeinfo(sub_info);
242    else
243        complete(sub_info->complete);
244    return 0;
245}
246
247/* This is run by khelper thread */
248static void __call_usermodehelper(struct work_struct *work)
249{
250    struct subprocess_info *sub_info =
251        container_of(work, struct subprocess_info, work);
252    pid_t pid;
253    enum umh_wait wait = sub_info->wait;
254
255    BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
256
257    /* CLONE_VFORK: wait until the usermode helper has execve'd
258     * successfully We need the data structures to stay around
259     * until that is done. */
260    if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
261        pid = kernel_thread(wait_for_helper, sub_info,
262                    CLONE_FS | CLONE_FILES | SIGCHLD);
263    else
264        pid = kernel_thread(____call_usermodehelper, sub_info,
265                    CLONE_VFORK | SIGCHLD);
266
267    switch (wait) {
268    case UMH_NO_WAIT:
269        break;
270
271    case UMH_WAIT_PROC:
272        if (pid > 0)
273            break;
274        sub_info->retval = pid;
275        /* FALLTHROUGH */
276
277    case UMH_WAIT_EXEC:
278        complete(sub_info->complete);
279    }
280}
281
282#ifdef CONFIG_PM_SLEEP
283/*
284 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
285 * (used for preventing user land processes from being created after the user
286 * land has been frozen during a system-wide hibernation or suspend operation).
287 */
288static int usermodehelper_disabled;
289
290/* Number of helpers running */
291static atomic_t running_helpers = ATOMIC_INIT(0);
292
293/*
294 * Wait queue head used by usermodehelper_pm_callback() to wait for all running
295 * helpers to finish.
296 */
297static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
298
299/*
300 * Time to wait for running_helpers to become zero before the setting of
301 * usermodehelper_disabled in usermodehelper_pm_callback() fails
302 */
303#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
304
305/**
306 * usermodehelper_disable - prevent new helpers from being started
307 */
308int usermodehelper_disable(void)
309{
310    long retval;
311
312    usermodehelper_disabled = 1;
313    smp_mb();
314    /*
315     * From now on call_usermodehelper_exec() won't start any new
316     * helpers, so it is sufficient if running_helpers turns out to
317     * be zero at one point (it may be increased later, but that
318     * doesn't matter).
319     */
320    retval = wait_event_timeout(running_helpers_waitq,
321                    atomic_read(&running_helpers) == 0,
322                    RUNNING_HELPERS_TIMEOUT);
323    if (retval)
324        return 0;
325
326    usermodehelper_disabled = 0;
327    return -EAGAIN;
328}
329
330/**
331 * usermodehelper_enable - allow new helpers to be started again
332 */
333void usermodehelper_enable(void)
334{
335    usermodehelper_disabled = 0;
336}
337
338static void helper_lock(void)
339{
340    atomic_inc(&running_helpers);
341    smp_mb__after_atomic_inc();
342}
343
344static void helper_unlock(void)
345{
346    if (atomic_dec_and_test(&running_helpers))
347        wake_up(&running_helpers_waitq);
348}
349#else /* CONFIG_PM_SLEEP */
350#define usermodehelper_disabled 0
351
352static inline void helper_lock(void) {}
353static inline void helper_unlock(void) {}
354#endif /* CONFIG_PM_SLEEP */
355
356/**
357 * call_usermodehelper_setup - prepare to call a usermode helper
358 * @path: path to usermode executable
359 * @argv: arg vector for process
360 * @envp: environment for process
361 * @gfp_mask: gfp mask for memory allocation
362 *
363 * Returns either %NULL on allocation failure, or a subprocess_info
364 * structure. This should be passed to call_usermodehelper_exec to
365 * exec the process and free the structure.
366 */
367struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
368                          char **envp, gfp_t gfp_mask)
369{
370    struct subprocess_info *sub_info;
371    sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
372    if (!sub_info)
373        goto out;
374
375    INIT_WORK(&sub_info->work, __call_usermodehelper);
376    sub_info->path = path;
377    sub_info->argv = argv;
378    sub_info->envp = envp;
379    sub_info->cred = prepare_usermodehelper_creds();
380    if (!sub_info->cred) {
381        kfree(sub_info);
382        return NULL;
383    }
384
385  out:
386    return sub_info;
387}
388EXPORT_SYMBOL(call_usermodehelper_setup);
389
390/**
391 * call_usermodehelper_setkeys - set the session keys for usermode helper
392 * @info: a subprocess_info returned by call_usermodehelper_setup
393 * @session_keyring: the session keyring for the process
394 */
395void call_usermodehelper_setkeys(struct subprocess_info *info,
396                 struct key *session_keyring)
397{
398#ifdef CONFIG_KEYS
399    struct thread_group_cred *tgcred = info->cred->tgcred;
400    key_put(tgcred->session_keyring);
401    tgcred->session_keyring = key_get(session_keyring);
402#else
403    BUG();
404#endif
405}
406EXPORT_SYMBOL(call_usermodehelper_setkeys);
407
408/**
409 * call_usermodehelper_setcleanup - set a cleanup function
410 * @info: a subprocess_info returned by call_usermodehelper_setup
411 * @cleanup: a cleanup function
412 *
413 * The cleanup function is just befor ethe subprocess_info is about to
414 * be freed. This can be used for freeing the argv and envp. The
415 * Function must be runnable in either a process context or the
416 * context in which call_usermodehelper_exec is called.
417 */
418void call_usermodehelper_setcleanup(struct subprocess_info *info,
419                    void (*cleanup)(char **argv, char **envp))
420{
421    info->cleanup = cleanup;
422}
423EXPORT_SYMBOL(call_usermodehelper_setcleanup);
424
425/**
426 * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
427 * @sub_info: a subprocess_info returned by call_usermodehelper_setup
428 * @filp: set to the write-end of a pipe
429 *
430 * This constructs a pipe, and sets the read end to be the stdin of the
431 * subprocess, and returns the write-end in *@filp.
432 */
433int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
434                  struct file **filp)
435{
436    struct file *f;
437
438    f = create_write_pipe(0);
439    if (IS_ERR(f))
440        return PTR_ERR(f);
441    *filp = f;
442
443    f = create_read_pipe(f, 0);
444    if (IS_ERR(f)) {
445        free_write_pipe(*filp);
446        return PTR_ERR(f);
447    }
448    sub_info->stdin = f;
449
450    return 0;
451}
452EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
453
454/**
455 * call_usermodehelper_exec - start a usermode application
456 * @sub_info: information about the subprocessa
457 * @wait: wait for the application to finish and return status.
458 * when -1 don't wait at all, but you get no useful error back when
459 * the program couldn't be exec'ed. This makes it safe to call
460 * from interrupt context.
461 *
462 * Runs a user-space application. The application is started
463 * asynchronously if wait is not set, and runs as a child of keventd.
464 * (ie. it runs with full root capabilities).
465 */
466int call_usermodehelper_exec(struct subprocess_info *sub_info,
467                 enum umh_wait wait)
468{
469    DECLARE_COMPLETION_ONSTACK(done);
470    int retval = 0;
471
472    BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
473    validate_creds(sub_info->cred);
474
475    helper_lock();
476    if (sub_info->path[0] == '\0')
477        goto out;
478
479    if (!khelper_wq || usermodehelper_disabled) {
480        retval = -EBUSY;
481        goto out;
482    }
483
484    sub_info->complete = &done;
485    sub_info->wait = wait;
486
487    queue_work(khelper_wq, &sub_info->work);
488    if (wait == UMH_NO_WAIT) /* task has freed sub_info */
489        goto unlock;
490    wait_for_completion(&done);
491    retval = sub_info->retval;
492
493out:
494    call_usermodehelper_freeinfo(sub_info);
495unlock:
496    helper_unlock();
497    return retval;
498}
499EXPORT_SYMBOL(call_usermodehelper_exec);
500
501/**
502 * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
503 * @path: path to usermode executable
504 * @argv: arg vector for process
505 * @envp: environment for process
506 * @filp: set to the write-end of a pipe
507 *
508 * This is a simple wrapper which executes a usermode-helper function
509 * with a pipe as stdin. It is implemented entirely in terms of
510 * lower-level call_usermodehelper_* functions.
511 */
512int call_usermodehelper_pipe(char *path, char **argv, char **envp,
513                 struct file **filp)
514{
515    struct subprocess_info *sub_info;
516    int ret;
517
518    sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
519    if (sub_info == NULL)
520        return -ENOMEM;
521
522    ret = call_usermodehelper_stdinpipe(sub_info, filp);
523    if (ret < 0) {
524        call_usermodehelper_freeinfo(sub_info);
525        return ret;
526    }
527
528    ret = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
529    if (ret < 0) /* Failed to execute helper, close pipe */
530        filp_close(*filp, NULL);
531
532    return ret;
533}
534EXPORT_SYMBOL(call_usermodehelper_pipe);
535
536void __init usermodehelper_init(void)
537{
538    khelper_wq = create_singlethread_workqueue("khelper");
539    BUG_ON(!khelper_wq);
540}
541

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