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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright(c) 2014 Intel Mobile Communications GmbH
4 * Copyright(c) 2015 Intel Deutschland GmbH
5 *
6 * Author: Johannes Berg <[email protected]>
7 */
8#include <linux/module.h>
9#include <linux/device.h>
10#include <linux/devcoredump.h>
11#include <linux/list.h>
12#include <linux/slab.h>
13#include <linux/fs.h>
14#include <linux/workqueue.h>
15
16static struct class devcd_class;
17
18/* global disable flag, for security purposes */
19static bool devcd_disabled;
20
21struct devcd_entry {
22 struct device devcd_dev;
23 void *data;
24 size_t datalen;
25 /*
26 * There are 2 races for which mutex is required.
27 *
28 * The first race is between device creation and userspace writing to
29 * schedule immediately destruction.
30 *
31 * This race is handled by arming the timer before device creation, but
32 * when device creation fails the timer still exists.
33 *
34 * To solve this, hold the mutex during device_add(), and set
35 * init_completed on success before releasing the mutex.
36 *
37 * That way the timer will never fire until device_add() is called,
38 * it will do nothing if init_completed is not set. The timer is also
39 * cancelled in that case.
40 *
41 * The second race involves multiple parallel invocations of devcd_free(),
42 * add a deleted flag so only 1 can call the destructor.
43 */
44 struct mutex mutex;
45 bool init_completed, deleted;
46 struct module *owner;
47 ssize_t (*read)(char *buffer, loff_t offset, size_t count,
48 void *data, size_t datalen);
49 void (*free)(void *data);
50 /*
51 * If nothing interferes and device_add() was returns success,
52 * del_wk will destroy the device after the timer fires.
53 *
54 * Multiple userspace processes can interfere in the working of the timer:
55 * - Writing to the coredump will reschedule the timer to run immediately,
56 * if still armed.
57 *
58 * This is handled by using "if (cancel_delayed_work()) {
59 * schedule_delayed_work() }", to prevent re-arming after having
60 * been previously fired.
61 * - Writing to /sys/class/devcoredump/disabled will destroy the
62 * coredump synchronously.
63 * This is handled by using disable_delayed_work_sync(), and then
64 * checking if deleted flag is set with &devcd->mutex held.
65 */
66 struct delayed_work del_wk;
67 struct device *failing_dev;
68};
69
70static struct devcd_entry *dev_to_devcd(struct device *dev)
71{
72 return container_of(dev, struct devcd_entry, devcd_dev);
73}
74
75static void devcd_dev_release(struct device *dev)
76{
77 struct devcd_entry *devcd = dev_to_devcd(dev);
78
79 devcd->free(devcd->data);
80 module_put(devcd->owner);
81
82 /*
83 * this seems racy, but I don't see a notifier or such on
84 * a struct device to know when it goes away?
85 */
86 if (devcd->failing_dev->kobj.sd)
87 sysfs_delete_link(&devcd->failing_dev->kobj, &dev->kobj,
88 "devcoredump");
89
90 put_device(devcd->failing_dev);
91 kfree(devcd);
92}
93
94static void __devcd_del(struct devcd_entry *devcd)
95{
96 devcd->deleted = true;
97 device_del(&devcd->devcd_dev);
98 put_device(&devcd->devcd_dev);
99}
100
101static void devcd_del(struct work_struct *wk)
102{
103 struct devcd_entry *devcd;
104 bool init_completed;
105
106 devcd = container_of(wk, struct devcd_entry, del_wk.work);
107
108 /* devcd->mutex serializes against dev_coredumpm_timeout */
109 mutex_lock(&devcd->mutex);
110 init_completed = devcd->init_completed;
111 mutex_unlock(&devcd->mutex);
112
113 if (init_completed)
114 __devcd_del(devcd);
115}
116
117static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj,
118 const struct bin_attribute *bin_attr,
119 char *buffer, loff_t offset, size_t count)
120{
121 struct device *dev = kobj_to_dev(kobj);
122 struct devcd_entry *devcd = dev_to_devcd(dev);
123
124 return devcd->read(buffer, offset, count, devcd->data, devcd->datalen);
125}
126
127static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
128 const struct bin_attribute *bin_attr,
129 char *buffer, loff_t offset, size_t count)
130{
131 struct device *dev = kobj_to_dev(kobj);
132 struct devcd_entry *devcd = dev_to_devcd(dev);
133
134 /*
135 * Although it's tempting to use mod_delayed work here,
136 * that will cause a reschedule if the timer already fired.
137 */
138 if (cancel_delayed_work(&devcd->del_wk))
139 schedule_delayed_work(&devcd->del_wk, 0);
140
141 return count;
142}
143
144static const struct bin_attribute devcd_attr_data =
145 __BIN_ATTR(data, 0600, devcd_data_read, devcd_data_write, 0);
146
147static const struct bin_attribute *const devcd_dev_bin_attrs[] = {
148 &devcd_attr_data, NULL,
149};
150
151static const struct attribute_group devcd_dev_group = {
152 .bin_attrs = devcd_dev_bin_attrs,
153};
154
155static const struct attribute_group *devcd_dev_groups[] = {
156 &devcd_dev_group, NULL,
157};
158
159static int devcd_free(struct device *dev, void *data)
160{
161 struct devcd_entry *devcd = dev_to_devcd(dev);
162
163 /*
164 * To prevent a race with devcd_data_write(), disable work and
165 * complete manually instead.
166 *
167 * We cannot rely on the return value of
168 * disable_delayed_work_sync() here, because it might be in the
169 * middle of a cancel_delayed_work + schedule_delayed_work pair.
170 *
171 * devcd->mutex here guards against multiple parallel invocations
172 * of devcd_free().
173 */
174 disable_delayed_work_sync(&devcd->del_wk);
175 mutex_lock(&devcd->mutex);
176 if (!devcd->deleted)
177 __devcd_del(devcd);
178 mutex_unlock(&devcd->mutex);
179 return 0;
180}
181
182static ssize_t disabled_show(const struct class *class, const struct class_attribute *attr,
183 char *buf)
184{
185 return sysfs_emit(buf, "%d\n", devcd_disabled);
186}
187
188/*
189 *
190 * disabled_store() worker()
191 * class_for_each_device(&devcd_class,
192 * NULL, NULL, devcd_free)
193 * ...
194 * ...
195 * while ((dev = class_dev_iter_next(&iter))
196 * devcd_del()
197 * device_del()
198 * put_device() <- last reference
199 * error = fn(dev, data) devcd_dev_release()
200 * devcd_free(dev, data) kfree(devcd)
201 *
202 *
203 * In the above diagram, it looks like disabled_store() would be racing with parallelly
204 * running devcd_del() and result in memory abort after dropping its last reference with
205 * put_device(). However, this will not happens as fn(dev, data) runs
206 * with its own reference to device via klist_node so it is not its last reference.
207 * so, above situation would not occur.
208 */
209
210static ssize_t disabled_store(const struct class *class, const struct class_attribute *attr,
211 const char *buf, size_t count)
212{
213 long tmp = simple_strtol(buf, NULL, 10);
214
215 /*
216 * This essentially makes the attribute write-once, since you can't
217 * go back to not having it disabled. This is intentional, it serves
218 * as a system lockdown feature.
219 */
220 if (tmp != 1)
221 return -EINVAL;
222
223 devcd_disabled = true;
224
225 class_for_each_device(&devcd_class, NULL, NULL, devcd_free);
226
227 return count;
228}
229static CLASS_ATTR_RW(disabled);
230
231static struct attribute *devcd_class_attrs[] = {
232 &class_attr_disabled.attr,
233 NULL,
234};
235ATTRIBUTE_GROUPS(devcd_class);
236
237static struct class devcd_class = {
238 .name = "devcoredump",
239 .dev_release = devcd_dev_release,
240 .dev_groups = devcd_dev_groups,
241 .class_groups = devcd_class_groups,
242};
243
244static ssize_t devcd_readv(char *buffer, loff_t offset, size_t count,
245 void *data, size_t datalen)
246{
247 return memory_read_from_buffer(buffer, count, &offset, data, datalen);
248}
249
250static void devcd_freev(void *data)
251{
252 vfree(data);
253}
254
255/**
256 * dev_coredumpv - create device coredump with vmalloc data
257 * @dev: the struct device for the crashed device
258 * @data: vmalloc data containing the device coredump
259 * @datalen: length of the data
260 * @gfp: allocation flags
261 *
262 * This function takes ownership of the vmalloc'ed data and will free
263 * it when it is no longer used. See dev_coredumpm() for more information.
264 */
265void dev_coredumpv(struct device *dev, void *data, size_t datalen,
266 gfp_t gfp)
267{
268 dev_coredumpm(dev, NULL, data, datalen, gfp, devcd_readv, devcd_freev);
269}
270EXPORT_SYMBOL_GPL(dev_coredumpv);
271
272static int devcd_match_failing(struct device *dev, const void *failing)
273{
274 struct devcd_entry *devcd = dev_to_devcd(dev);
275
276 return devcd->failing_dev == failing;
277}
278
279/**
280 * devcd_free_sgtable - free all the memory of the given scatterlist table
281 * (i.e. both pages and scatterlist instances)
282 * NOTE: if two tables allocated with devcd_alloc_sgtable and then chained
283 * using the sg_chain function then that function should be called only once
284 * on the chained table
285 * @data: pointer to sg_table to free
286 */
287static void devcd_free_sgtable(void *data)
288{
289 _devcd_free_sgtable(data);
290}
291
292/**
293 * devcd_read_from_sgtable - copy data from sg_table to a given buffer
294 * and return the number of bytes read
295 * @buffer: the buffer to copy the data to it
296 * @buf_len: the length of the buffer
297 * @data: the scatterlist table to copy from
298 * @offset: start copy from @offset@ bytes from the head of the data
299 * in the given scatterlist
300 * @data_len: the length of the data in the sg_table
301 *
302 * Returns: the number of bytes copied
303 */
304static ssize_t devcd_read_from_sgtable(char *buffer, loff_t offset,
305 size_t buf_len, void *data,
306 size_t data_len)
307{
308 struct scatterlist *table = data;
309
310 if (offset > data_len)
311 return -EINVAL;
312
313 if (offset + buf_len > data_len)
314 buf_len = data_len - offset;
315 return sg_pcopy_to_buffer(table, sg_nents(table), buffer, buf_len,
316 offset);
317}
318
319/**
320 * dev_coredump_put - remove device coredump
321 * @dev: the struct device for the crashed device
322 *
323 * dev_coredump_put() removes coredump, if exists, for a given device from
324 * the file system and free its associated data otherwise, does nothing.
325 *
326 * It is useful for modules that do not want to keep coredump
327 * available after its unload.
328 */
329void dev_coredump_put(struct device *dev)
330{
331 struct device *existing;
332
333 existing = class_find_device(&devcd_class, NULL, dev,
334 devcd_match_failing);
335 if (existing) {
336 devcd_free(existing, NULL);
337 put_device(existing);
338 }
339}
340EXPORT_SYMBOL_GPL(dev_coredump_put);
341
342/**
343 * dev_coredumpm_timeout - create device coredump with read/free methods with a
344 * custom timeout.
345 * @dev: the struct device for the crashed device
346 * @owner: the module that contains the read/free functions, use %THIS_MODULE
347 * @data: data cookie for the @read/@free functions
348 * @datalen: length of the data
349 * @gfp: allocation flags
350 * @read: function to read from the given buffer
351 * @free: function to free the given buffer
352 * @timeout: time in jiffies to remove coredump
353 *
354 * Creates a new device coredump for the given device. If a previous one hasn't
355 * been read yet, the new coredump is discarded. The data lifetime is determined
356 * by the device coredump framework and when it is no longer needed the @free
357 * function will be called to free the data.
358 */
359void dev_coredumpm_timeout(struct device *dev, struct module *owner,
360 void *data, size_t datalen, gfp_t gfp,
361 ssize_t (*read)(char *buffer, loff_t offset,
362 size_t count, void *data,
363 size_t datalen),
364 void (*free)(void *data),
365 unsigned long timeout)
366{
367 static atomic_t devcd_count = ATOMIC_INIT(0);
368 struct devcd_entry *devcd;
369 struct device *existing;
370
371 if (devcd_disabled)
372 goto free;
373
374 existing = class_find_device(&devcd_class, NULL, dev,
375 devcd_match_failing);
376 if (existing) {
377 put_device(existing);
378 goto free;
379 }
380
381 if (!try_module_get(owner))
382 goto free;
383
384 devcd = kzalloc_obj(*devcd, gfp);
385 if (!devcd)
386 goto put_module;
387
388 devcd->owner = owner;
389 devcd->data = data;
390 devcd->datalen = datalen;
391 devcd->read = read;
392 devcd->free = free;
393 devcd->failing_dev = get_device(dev);
394 devcd->deleted = false;
395
396 mutex_init(&devcd->mutex);
397 device_initialize(&devcd->devcd_dev);
398
399 dev_set_name(&devcd->devcd_dev, "devcd%d",
400 atomic_inc_return(&devcd_count));
401 devcd->devcd_dev.class = &devcd_class;
402
403 dev_set_uevent_suppress(&devcd->devcd_dev, true);
404
405 /* devcd->mutex prevents devcd_del() completing until init finishes */
406 mutex_lock(&devcd->mutex);
407 devcd->init_completed = false;
408 INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
409 schedule_delayed_work(&devcd->del_wk, timeout);
410
411 if (device_add(&devcd->devcd_dev))
412 goto put_device;
413
414 /*
415 * These should normally not fail, but there is no problem
416 * continuing without the links, so just warn instead of
417 * failing.
418 */
419 if (sysfs_create_link(&devcd->devcd_dev.kobj, &dev->kobj,
420 "failing_device") ||
421 sysfs_create_link(&dev->kobj, &devcd->devcd_dev.kobj,
422 "devcoredump"))
423 dev_warn(dev, "devcoredump create_link failed\n");
424
425 dev_set_uevent_suppress(&devcd->devcd_dev, false);
426 kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD);
427
428 /*
429 * Safe to run devcd_del() now that we are done with devcd_dev.
430 * Alternatively we could have taken a ref on devcd_dev before
431 * dropping the lock.
432 */
433 devcd->init_completed = true;
434 mutex_unlock(&devcd->mutex);
435 return;
436 put_device:
437 mutex_unlock(&devcd->mutex);
438 cancel_delayed_work_sync(&devcd->del_wk);
439 put_device(&devcd->devcd_dev);
440
441 put_module:
442 module_put(owner);
443 free:
444 free(data);
445}
446EXPORT_SYMBOL_GPL(dev_coredumpm_timeout);
447
448/**
449 * dev_coredumpsg - create device coredump that uses scatterlist as data
450 * parameter
451 * @dev: the struct device for the crashed device
452 * @table: the dump data
453 * @datalen: length of the data
454 * @gfp: allocation flags
455 *
456 * Creates a new device coredump for the given device. If a previous one hasn't
457 * been read yet, the new coredump is discarded. The data lifetime is determined
458 * by the device coredump framework and when it is no longer needed
459 * it will free the data.
460 */
461void dev_coredumpsg(struct device *dev, struct scatterlist *table,
462 size_t datalen, gfp_t gfp)
463{
464 dev_coredumpm(dev, NULL, table, datalen, gfp, devcd_read_from_sgtable,
465 devcd_free_sgtable);
466}
467EXPORT_SYMBOL_GPL(dev_coredumpsg);
468
469static int __init devcoredump_init(void)
470{
471 return class_register(&devcd_class);
472}
473__initcall(devcoredump_init);