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/cred.h>
29#include <linux/file.h>
30#include <linux/fdtable.h>
31#include <linux/workqueue.h>
32#include <linux/security.h>
33#include <linux/mount.h>
34#include <linux/kernel.h>
35#include <linux/init.h>
36#include <linux/resource.h>
37#include <linux/notifier.h>
38#include <linux/suspend.h>
39#include <linux/rwsem.h>
40#include <asm/uaccess.h>
41
42#include <trace/events/module.h>
43
44extern int max_threads;
45
46static struct workqueue_struct *khelper_wq;
47
48#define CAP_BSET (void *)1
49#define CAP_PI (void *)2
50
51static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
52static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
53static DEFINE_SPINLOCK(umh_sysctl_lock);
54static DECLARE_RWSEM(umhelper_sem);
55
56#ifdef CONFIG_MODULES
57
58/*
59    modprobe_path is set via /proc/sys.
60*/
61char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
62
63static void free_modprobe_argv(struct subprocess_info *info)
64{
65    kfree(info->argv[3]); /* check call_modprobe() */
66    kfree(info->argv);
67}
68
69static int call_modprobe(char *module_name, int wait)
70{
71    static char *envp[] = {
72        "HOME=/",
73        "TERM=linux",
74        "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
75        NULL
76    };
77
78    char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
79    if (!argv)
80        goto out;
81
82    module_name = kstrdup(module_name, GFP_KERNEL);
83    if (!module_name)
84        goto free_argv;
85
86    argv[0] = modprobe_path;
87    argv[1] = "-q";
88    argv[2] = "--";
89    argv[3] = module_name; /* check free_modprobe_argv() */
90    argv[4] = NULL;
91
92    return call_usermodehelper_fns(modprobe_path, argv, envp,
93        wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
94free_argv:
95    kfree(argv);
96out:
97    return -ENOMEM;
98}
99
100/**
101 * __request_module - try to load a kernel module
102 * @wait: wait (or not) for the operation to complete
103 * @fmt: printf style format string for the name of the module
104 * @...: arguments as specified in the format string
105 *
106 * Load a module using the user mode module loader. The function returns
107 * zero on success or a negative errno code on failure. Note that a
108 * successful module load does not mean the module did not then unload
109 * and exit on an error of its own. Callers must check that the service
110 * they requested is now available not blindly invoke it.
111 *
112 * If module auto-loading support is disabled then this function
113 * becomes a no-operation.
114 */
115int __request_module(bool wait, const char *fmt, ...)
116{
117    va_list args;
118    char module_name[MODULE_NAME_LEN];
119    unsigned int max_modprobes;
120    int ret;
121    static atomic_t kmod_concurrent = ATOMIC_INIT(0);
122#define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */
123    static int kmod_loop_msg;
124
125    va_start(args, fmt);
126    ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
127    va_end(args);
128    if (ret >= MODULE_NAME_LEN)
129        return -ENAMETOOLONG;
130
131    ret = security_kernel_module_request(module_name);
132    if (ret)
133        return ret;
134
135    /* If modprobe needs a service that is in a module, we get a recursive
136     * loop. Limit the number of running kmod threads to max_threads/2 or
137     * MAX_KMOD_CONCURRENT, whichever is the smaller. A cleaner method
138     * would be to run the parents of this process, counting how many times
139     * kmod was invoked. That would mean accessing the internals of the
140     * process tables to get the command line, proc_pid_cmdline is static
141     * and it is not worth changing the proc code just to handle this case.
142     * KAO.
143     *
144     * "trace the ppid" is simple, but will fail if someone's
145     * parent exits. I think this is as good as it gets. --RR
146     */
147    max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
148    atomic_inc(&kmod_concurrent);
149    if (atomic_read(&kmod_concurrent) > max_modprobes) {
150        /* We may be blaming an innocent here, but unlikely */
151        if (kmod_loop_msg < 5) {
152            printk(KERN_ERR
153                   "request_module: runaway loop modprobe %s\n",
154                   module_name);
155            kmod_loop_msg++;
156        }
157        atomic_dec(&kmod_concurrent);
158        return -ENOMEM;
159    }
160
161    trace_module_request(module_name, wait, _RET_IP_);
162
163    ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
164
165    atomic_dec(&kmod_concurrent);
166    return ret;
167}
168EXPORT_SYMBOL(__request_module);
169#endif /* CONFIG_MODULES */
170
171/*
172 * This is the task which runs the usermode application
173 */
174static int ____call_usermodehelper(void *data)
175{
176    struct subprocess_info *sub_info = data;
177    struct cred *new;
178    int retval;
179
180    spin_lock_irq(&current->sighand->siglock);
181    flush_signal_handlers(current, 1);
182    spin_unlock_irq(&current->sighand->siglock);
183
184    /* We can run anywhere, unlike our parent keventd(). */
185    set_cpus_allowed_ptr(current, cpu_all_mask);
186
187    /*
188     * Our parent is keventd, which runs with elevated scheduling priority.
189     * Avoid propagating that into the userspace child.
190     */
191    set_user_nice(current, 0);
192
193    retval = -ENOMEM;
194    new = prepare_kernel_cred(current);
195    if (!new)
196        goto fail;
197
198    spin_lock(&umh_sysctl_lock);
199    new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
200    new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
201                         new->cap_inheritable);
202    spin_unlock(&umh_sysctl_lock);
203
204    if (sub_info->init) {
205        retval = sub_info->init(sub_info, new);
206        if (retval) {
207            abort_creds(new);
208            goto fail;
209        }
210    }
211
212    commit_creds(new);
213
214    retval = kernel_execve(sub_info->path,
215                   (const char *const *)sub_info->argv,
216                   (const char *const *)sub_info->envp);
217
218    /* Exec failed? */
219fail:
220    sub_info->retval = retval;
221    return 0;
222}
223
224static void call_usermodehelper_freeinfo(struct subprocess_info *info)
225{
226    if (info->cleanup)
227        (*info->cleanup)(info);
228    kfree(info);
229}
230
231static void umh_complete(struct subprocess_info *sub_info)
232{
233    struct completion *comp = xchg(&sub_info->complete, NULL);
234    /*
235     * See call_usermodehelper_exec(). If xchg() returns NULL
236     * we own sub_info, the UMH_KILLABLE caller has gone away.
237     */
238    if (comp)
239        complete(comp);
240    else
241        call_usermodehelper_freeinfo(sub_info);
242}
243
244/* Keventd can't block, but this (a child) can. */
245static int wait_for_helper(void *data)
246{
247    struct subprocess_info *sub_info = data;
248    pid_t pid;
249
250    /* If SIGCLD is ignored sys_wait4 won't populate the status. */
251    spin_lock_irq(&current->sighand->siglock);
252    current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
253    spin_unlock_irq(&current->sighand->siglock);
254
255    pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
256    if (pid < 0) {
257        sub_info->retval = pid;
258    } else {
259        int ret = -ECHILD;
260        /*
261         * Normally it is bogus to call wait4() from in-kernel because
262         * wait4() wants to write the exit code to a userspace address.
263         * But wait_for_helper() always runs as keventd, and put_user()
264         * to a kernel address works OK for kernel threads, due to their
265         * having an mm_segment_t which spans the entire address space.
266         *
267         * Thus the __user pointer cast is valid here.
268         */
269        sys_wait4(pid, (int __user *)&ret, 0, NULL);
270
271        /*
272         * If ret is 0, either ____call_usermodehelper failed and the
273         * real error code is already in sub_info->retval or
274         * sub_info->retval is 0 anyway, so don't mess with it then.
275         */
276        if (ret)
277            sub_info->retval = ret;
278    }
279
280    umh_complete(sub_info);
281    return 0;
282}
283
284/* This is run by khelper thread */
285static void __call_usermodehelper(struct work_struct *work)
286{
287    struct subprocess_info *sub_info =
288        container_of(work, struct subprocess_info, work);
289    int wait = sub_info->wait & ~UMH_KILLABLE;
290    pid_t pid;
291
292    /* CLONE_VFORK: wait until the usermode helper has execve'd
293     * successfully We need the data structures to stay around
294     * until that is done. */
295    if (wait == UMH_WAIT_PROC)
296        pid = kernel_thread(wait_for_helper, sub_info,
297                    CLONE_FS | CLONE_FILES | SIGCHLD);
298    else
299        pid = kernel_thread(____call_usermodehelper, sub_info,
300                    CLONE_VFORK | SIGCHLD);
301
302    switch (wait) {
303    case UMH_NO_WAIT:
304        call_usermodehelper_freeinfo(sub_info);
305        break;
306
307    case UMH_WAIT_PROC:
308        if (pid > 0)
309            break;
310        /* FALLTHROUGH */
311    case UMH_WAIT_EXEC:
312        if (pid < 0)
313            sub_info->retval = pid;
314        umh_complete(sub_info);
315    }
316}
317
318/*
319 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
320 * (used for preventing user land processes from being created after the user
321 * land has been frozen during a system-wide hibernation or suspend operation).
322 * Should always be manipulated under umhelper_sem acquired for write.
323 */
324static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
325
326/* Number of helpers running */
327static atomic_t running_helpers = ATOMIC_INIT(0);
328
329/*
330 * Wait queue head used by usermodehelper_disable() to wait for all running
331 * helpers to finish.
332 */
333static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
334
335/*
336 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
337 * to become 'false'.
338 */
339static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
340
341/*
342 * Time to wait for running_helpers to become zero before the setting of
343 * usermodehelper_disabled in usermodehelper_disable() fails
344 */
345#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
346
347int usermodehelper_read_trylock(void)
348{
349    DEFINE_WAIT(wait);
350    int ret = 0;
351
352    down_read(&umhelper_sem);
353    for (;;) {
354        prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
355                TASK_INTERRUPTIBLE);
356        if (!usermodehelper_disabled)
357            break;
358
359        if (usermodehelper_disabled == UMH_DISABLED)
360            ret = -EAGAIN;
361
362        up_read(&umhelper_sem);
363
364        if (ret)
365            break;
366
367        schedule();
368        try_to_freeze();
369
370        down_read(&umhelper_sem);
371    }
372    finish_wait(&usermodehelper_disabled_waitq, &wait);
373    return ret;
374}
375EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
376
377long usermodehelper_read_lock_wait(long timeout)
378{
379    DEFINE_WAIT(wait);
380
381    if (timeout < 0)
382        return -EINVAL;
383
384    down_read(&umhelper_sem);
385    for (;;) {
386        prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
387                TASK_UNINTERRUPTIBLE);
388        if (!usermodehelper_disabled)
389            break;
390
391        up_read(&umhelper_sem);
392
393        timeout = schedule_timeout(timeout);
394        if (!timeout)
395            break;
396
397        down_read(&umhelper_sem);
398    }
399    finish_wait(&usermodehelper_disabled_waitq, &wait);
400    return timeout;
401}
402EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
403
404void usermodehelper_read_unlock(void)
405{
406    up_read(&umhelper_sem);
407}
408EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
409
410/**
411 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
412 * @depth: New value to assign to usermodehelper_disabled.
413 *
414 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
415 * writing) and wakeup tasks waiting for it to change.
416 */
417void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
418{
419    down_write(&umhelper_sem);
420    usermodehelper_disabled = depth;
421    wake_up(&usermodehelper_disabled_waitq);
422    up_write(&umhelper_sem);
423}
424
425/**
426 * __usermodehelper_disable - Prevent new helpers from being started.
427 * @depth: New value to assign to usermodehelper_disabled.
428 *
429 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
430 */
431int __usermodehelper_disable(enum umh_disable_depth depth)
432{
433    long retval;
434
435    if (!depth)
436        return -EINVAL;
437
438    down_write(&umhelper_sem);
439    usermodehelper_disabled = depth;
440    up_write(&umhelper_sem);
441
442    /*
443     * From now on call_usermodehelper_exec() won't start any new
444     * helpers, so it is sufficient if running_helpers turns out to
445     * be zero at one point (it may be increased later, but that
446     * doesn't matter).
447     */
448    retval = wait_event_timeout(running_helpers_waitq,
449                    atomic_read(&running_helpers) == 0,
450                    RUNNING_HELPERS_TIMEOUT);
451    if (retval)
452        return 0;
453
454    __usermodehelper_set_disable_depth(UMH_ENABLED);
455    return -EAGAIN;
456}
457
458static void helper_lock(void)
459{
460    atomic_inc(&running_helpers);
461    smp_mb__after_atomic_inc();
462}
463
464static void helper_unlock(void)
465{
466    if (atomic_dec_and_test(&running_helpers))
467        wake_up(&running_helpers_waitq);
468}
469
470/**
471 * call_usermodehelper_setup - prepare to call a usermode helper
472 * @path: path to usermode executable
473 * @argv: arg vector for process
474 * @envp: environment for process
475 * @gfp_mask: gfp mask for memory allocation
476 *
477 * Returns either %NULL on allocation failure, or a subprocess_info
478 * structure. This should be passed to call_usermodehelper_exec to
479 * exec the process and free the structure.
480 */
481static
482struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
483                          char **envp, gfp_t gfp_mask)
484{
485    struct subprocess_info *sub_info;
486    sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
487    if (!sub_info)
488        goto out;
489
490    INIT_WORK(&sub_info->work, __call_usermodehelper);
491    sub_info->path = path;
492    sub_info->argv = argv;
493    sub_info->envp = envp;
494  out:
495    return sub_info;
496}
497
498/**
499 * call_usermodehelper_setfns - set a cleanup/init function
500 * @info: a subprocess_info returned by call_usermodehelper_setup
501 * @cleanup: a cleanup function
502 * @init: an init function
503 * @data: arbitrary context sensitive data
504 *
505 * The init function is used to customize the helper process prior to
506 * exec. A non-zero return code causes the process to error out, exit,
507 * and return the failure to the calling process
508 *
509 * The cleanup function is just before ethe subprocess_info is about to
510 * be freed. This can be used for freeing the argv and envp. The
511 * Function must be runnable in either a process context or the
512 * context in which call_usermodehelper_exec is called.
513 */
514static
515void call_usermodehelper_setfns(struct subprocess_info *info,
516            int (*init)(struct subprocess_info *info, struct cred *new),
517            void (*cleanup)(struct subprocess_info *info),
518            void *data)
519{
520    info->cleanup = cleanup;
521    info->init = init;
522    info->data = data;
523}
524
525/**
526 * call_usermodehelper_exec - start a usermode application
527 * @sub_info: information about the subprocessa
528 * @wait: wait for the application to finish and return status.
529 * when -1 don't wait at all, but you get no useful error back when
530 * the program couldn't be exec'ed. This makes it safe to call
531 * from interrupt context.
532 *
533 * Runs a user-space application. The application is started
534 * asynchronously if wait is not set, and runs as a child of keventd.
535 * (ie. it runs with full root capabilities).
536 */
537static
538int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
539{
540    DECLARE_COMPLETION_ONSTACK(done);
541    int retval = 0;
542
543    helper_lock();
544    if (sub_info->path[0] == '\0')
545        goto out;
546
547    if (!khelper_wq || usermodehelper_disabled) {
548        retval = -EBUSY;
549        goto out;
550    }
551
552    sub_info->complete = &done;
553    sub_info->wait = wait;
554
555    queue_work(khelper_wq, &sub_info->work);
556    if (wait == UMH_NO_WAIT) /* task has freed sub_info */
557        goto unlock;
558
559    if (wait & UMH_KILLABLE) {
560        retval = wait_for_completion_killable(&done);
561        if (!retval)
562            goto wait_done;
563
564        /* umh_complete() will see NULL and free sub_info */
565        if (xchg(&sub_info->complete, NULL))
566            goto unlock;
567        /* fallthrough, umh_complete() was already called */
568    }
569
570    wait_for_completion(&done);
571wait_done:
572    retval = sub_info->retval;
573out:
574    call_usermodehelper_freeinfo(sub_info);
575unlock:
576    helper_unlock();
577    return retval;
578}
579
580int call_usermodehelper_fns(
581    char *path, char **argv, char **envp, int wait,
582    int (*init)(struct subprocess_info *info, struct cred *new),
583    void (*cleanup)(struct subprocess_info *), void *data)
584{
585    struct subprocess_info *info;
586    gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
587
588    info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
589
590    if (info == NULL)
591        return -ENOMEM;
592
593    call_usermodehelper_setfns(info, init, cleanup, data);
594
595    return call_usermodehelper_exec(info, wait);
596}
597EXPORT_SYMBOL(call_usermodehelper_fns);
598
599static int proc_cap_handler(struct ctl_table *table, int write,
600             void __user *buffer, size_t *lenp, loff_t *ppos)
601{
602    struct ctl_table t;
603    unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
604    kernel_cap_t new_cap;
605    int err, i;
606
607    if (write && (!capable(CAP_SETPCAP) ||
608              !capable(CAP_SYS_MODULE)))
609        return -EPERM;
610
611    /*
612     * convert from the global kernel_cap_t to the ulong array to print to
613     * userspace if this is a read.
614     */
615    spin_lock(&umh_sysctl_lock);
616    for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
617        if (table->data == CAP_BSET)
618            cap_array[i] = usermodehelper_bset.cap[i];
619        else if (table->data == CAP_PI)
620            cap_array[i] = usermodehelper_inheritable.cap[i];
621        else
622            BUG();
623    }
624    spin_unlock(&umh_sysctl_lock);
625
626    t = *table;
627    t.data = &cap_array;
628
629    /*
630     * actually read or write and array of ulongs from userspace. Remember
631     * these are least significant 32 bits first
632     */
633    err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
634    if (err < 0)
635        return err;
636
637    /*
638     * convert from the sysctl array of ulongs to the kernel_cap_t
639     * internal representation
640     */
641    for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
642        new_cap.cap[i] = cap_array[i];
643
644    /*
645     * Drop everything not in the new_cap (but don't add things)
646     */
647    spin_lock(&umh_sysctl_lock);
648    if (write) {
649        if (table->data == CAP_BSET)
650            usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
651        if (table->data == CAP_PI)
652            usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
653    }
654    spin_unlock(&umh_sysctl_lock);
655
656    return 0;
657}
658
659struct ctl_table usermodehelper_table[] = {
660    {
661        .procname = "bset",
662        .data = CAP_BSET,
663        .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
664        .mode = 0600,
665        .proc_handler = proc_cap_handler,
666    },
667    {
668        .procname = "inheritable",
669        .data = CAP_PI,
670        .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
671        .mode = 0600,
672        .proc_handler = proc_cap_handler,
673    },
674    { }
675};
676
677void __init usermodehelper_init(void)
678{
679    khelper_wq = create_singlethread_workqueue("khelper");
680    BUG_ON(!khelper_wq);
681}
682

Archive Download this file



interactive