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

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