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