drivers/base/devcoredump.c

   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 <johannes@sipsolutions.net>
   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
  16 static struct class devcd_class;
  17
  18 /* global disable flag, for security purposes */
  19 static bool devcd_disabled;
  20
  21 /* if data isn't read by userspace after 5 minutes then delete it */
  22 #define DEVCD_TIMEOUT   (HZ * 60 * 5)
  23
  24 struct devcd_entry {
  25         struct device devcd_dev;
  26         void *data;
  27         size_t datalen;
  28         /*
  29          * Here, mutex is required to serialize the calls to del_wk work between
  30          * user/kernel space which happens when devcd is added with device_add()
  31          * and that sends uevent to user space. User space reads the uevents,
  32          * and calls to devcd_data_write() which try to modify the work which is
  33          * not even initialized/queued from devcoredump.
  34          *
  35          *
  36          *
  37          *        cpu0(X)                                 cpu1(Y)
  38          *
  39          *        dev_coredump() uevent sent to user space
  40          *        device_add()  ======================> user space process Y reads the
  41          *                                              uevents writes to devcd fd
  42          *                                              which results into writes to
  43          *
  44          *                                             devcd_data_write()
  45          *                                               mod_delayed_work()
  46          *                                                 try_to_grab_pending()
  47          *                                                   del_timer()
  48          *                                                     debug_assert_init()
  49          *       INIT_DELAYED_WORK()
  50          *       schedule_delayed_work()
  51          *
  52          *
  53          * Also, mutex alone would not be enough to avoid scheduling of
  54          * del_wk work after it get flush from a call to devcd_free()
  55          * mentioned as below.
  56          *
  57          *      disabled_store()
  58          *        devcd_free()
  59          *          mutex_lock()             devcd_data_write()
  60          *          flush_delayed_work()
  61          *          mutex_unlock()
  62          *                                   mutex_lock()
  63          *                                   mod_delayed_work()
  64          *                                   mutex_unlock()
  65          * So, delete_work flag is required.
  66          */
  67         struct mutex mutex;
  68         bool delete_work;
  69         struct module *owner;
  70         ssize_t (*read)(char *buffer, loff_t offset, size_t count,
  71                         void *data, size_t datalen);
  72         void (*free)(void *data);
  73         struct delayed_work del_wk;
  74         struct device *failing_dev;
  75 };
  76
  77 static struct devcd_entry *dev_to_devcd(struct device *dev)
  78 {
  79         return container_of(dev, struct devcd_entry, devcd_dev);
  80 }
  81
  82 static void devcd_dev_release(struct device *dev)
  83 {
  84         struct devcd_entry *devcd = dev_to_devcd(dev);
  85
  86         devcd->free(devcd->data);
  87         module_put(devcd->owner);
  88
  89         /*
  90          * this seems racy, but I don't see a notifier or such on
  91          * a struct device to know when it goes away?
  92          */
  93         if (devcd->failing_dev->kobj.sd)
  94                 sysfs_delete_link(&devcd->failing_dev->kobj, &dev->kobj,
  95                                   "devcoredump");
  96
  97         put_device(devcd->failing_dev);
  98         kfree(devcd);
  99 }
 100
 101 static void devcd_del(struct work_struct *wk)
 102 {
 103         struct devcd_entry *devcd;
 104
 105         devcd = container_of(wk, struct devcd_entry, del_wk.work);
 106
 107         device_del(&devcd->devcd_dev);
 108         put_device(&devcd->devcd_dev);
 109 }
 110
 111 static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj,
 112                                struct bin_attribute *bin_attr,
 113                                char *buffer, loff_t offset, size_t count)
 114 {
 115         struct device *dev = kobj_to_dev(kobj);
 116         struct devcd_entry *devcd = dev_to_devcd(dev);
 117
 118         return devcd->read(buffer, offset, count, devcd->data, devcd->datalen);
 119 }
 120
 121 static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
 122                                 struct bin_attribute *bin_attr,
 123                                 char *buffer, loff_t offset, size_t count)
 124 {
 125         struct device *dev = kobj_to_dev(kobj);
 126         struct devcd_entry *devcd = dev_to_devcd(dev);
 127
 128         mutex_lock(&devcd->mutex);
 129         if (!devcd->delete_work) {
 130                 devcd->delete_work = true;
 131                 mod_delayed_work(system_wq, &devcd->del_wk, 0);
 132         }
 133         mutex_unlock(&devcd->mutex);
 134
 135         return count;
 136 }
 137
 138 static struct bin_attribute devcd_attr_data = {
 139         .attr = { .name = "data", .mode = S_IRUSR | S_IWUSR, },
 140         .size = 0,
 141         .read = devcd_data_read,
 142         .write = devcd_data_write,
 143 };
 144
 145 static struct bin_attribute *devcd_dev_bin_attrs[] = {
 146         &devcd_attr_data, NULL,
 147 };
 148
 149 static const struct attribute_group devcd_dev_group = {
 150         .bin_attrs = devcd_dev_bin_attrs,
 151 };
 152
 153 static const struct attribute_group *devcd_dev_groups[] = {
 154         &devcd_dev_group, NULL,
 155 };
 156
 157 static int devcd_free(struct device *dev, void *data)
 158 {
 159         struct devcd_entry *devcd = dev_to_devcd(dev);
 160
 161         mutex_lock(&devcd->mutex);
 162         if (!devcd->delete_work)
 163                 devcd->delete_work = true;
 164
 165         flush_delayed_work(&devcd->del_wk);
 166         mutex_unlock(&devcd->mutex);
 167         return 0;
 168 }
 169
 170 static ssize_t disabled_show(const struct class *class, const struct class_attribute *attr,
 171                              char *buf)
 172 {
 173         return sysfs_emit(buf, "%d\n", devcd_disabled);
 174 }
 175
 176 /*
 177  *
 178  *      disabled_store()                                        worker()
 179  *       class_for_each_device(&devcd_class,
 180  *              NULL, NULL, devcd_free)
 181  *         ...
 182  *         ...
 183  *         while ((dev = class_dev_iter_next(&iter))
 184  *                                                             devcd_del()
 185  *                                                               device_del()
 186  *                                                                 put_device() <- last reference
 187  *             error = fn(dev, data)                           devcd_dev_release()
 188  *             devcd_free(dev, data)                           kfree(devcd)
 189  *             mutex_lock(&devcd->mutex);
 190  *
 191  *
 192  * In the above diagram, It looks like disabled_store() would be racing with parallely
 193  * running devcd_del() and result in memory abort while acquiring devcd->mutex which
 194  * is called after kfree of devcd memory  after dropping its last reference with
 195  * put_device(). However, this will not happens as fn(dev, data) runs
 196  * with its own reference to device via klist_node so it is not its last reference.
 197  * so, above situation would not occur.
 198  */
 199
 200 static ssize_t disabled_store(const struct class *class, const struct class_attribute *attr,
 201                               const char *buf, size_t count)
 202 {
 203         long tmp = simple_strtol(buf, NULL, 10);
 204
 205         /*
 206          * This essentially makes the attribute write-once, since you can't
 207          * go back to not having it disabled. This is intentional, it serves
 208          * as a system lockdown feature.
 209          */
 210         if (tmp != 1)
 211                 return -EINVAL;
 212
 213         devcd_disabled = true;
 214
 215         class_for_each_device(&devcd_class, NULL, NULL, devcd_free);
 216
 217         return count;
 218 }
 219 static CLASS_ATTR_RW(disabled);
 220
 221 static struct attribute *devcd_class_attrs[] = {
 222         &class_attr_disabled.attr,
 223         NULL,
 224 };
 225 ATTRIBUTE_GROUPS(devcd_class);
 226
 227 static struct class devcd_class = {
 228         .name           = "devcoredump",
 229         .dev_release    = devcd_dev_release,
 230         .dev_groups     = devcd_dev_groups,
 231         .class_groups   = devcd_class_groups,
 232 };
 233
 234 static ssize_t devcd_readv(char *buffer, loff_t offset, size_t count,
 235                            void *data, size_t datalen)
 236 {
 237         return memory_read_from_buffer(buffer, count, &offset, data, datalen);
 238 }
 239
 240 static void devcd_freev(void *data)
 241 {
 242         vfree(data);
 243 }
 244
 245 /**
 246  * dev_coredumpv - create device coredump with vmalloc data
 247  * @dev: the struct device for the crashed device
 248  * @data: vmalloc data containing the device coredump
 249  * @datalen: length of the data
 250  * @gfp: allocation flags
 251  *
 252  * This function takes ownership of the vmalloc'ed data and will free
 253  * it when it is no longer used. See dev_coredumpm() for more information.
 254  */
 255 void dev_coredumpv(struct device *dev, void *data, size_t datalen,
 256                    gfp_t gfp)
 257 {
 258         dev_coredumpm(dev, NULL, data, datalen, gfp, devcd_readv, devcd_freev);
 259 }
 260 EXPORT_SYMBOL_GPL(dev_coredumpv);
 261
 262 static int devcd_match_failing(struct device *dev, const void *failing)
 263 {
 264         struct devcd_entry *devcd = dev_to_devcd(dev);
 265
 266         return devcd->failing_dev == failing;
 267 }
 268
 269 /**
 270  * devcd_free_sgtable - free all the memory of the given scatterlist table
 271  * (i.e. both pages and scatterlist instances)
 272  * NOTE: if two tables allocated with devcd_alloc_sgtable and then chained
 273  * using the sg_chain function then that function should be called only once
 274  * on the chained table
 275  * @data: pointer to sg_table to free
 276  */
 277 static void devcd_free_sgtable(void *data)
 278 {
 279         _devcd_free_sgtable(data);
 280 }
 281
 282 /**
 283  * devcd_read_from_sgtable - copy data from sg_table to a given buffer
 284  * and return the number of bytes read
 285  * @buffer: the buffer to copy the data to it
 286  * @buf_len: the length of the buffer
 287  * @data: the scatterlist table to copy from
 288  * @offset: start copy from @offset@ bytes from the head of the data
 289  *      in the given scatterlist
 290  * @data_len: the length of the data in the sg_table
 291  */
 292 static ssize_t devcd_read_from_sgtable(char *buffer, loff_t offset,
 293                                        size_t buf_len, void *data,
 294                                        size_t data_len)
 295 {
 296         struct scatterlist *table = data;
 297
 298         if (offset > data_len)
 299                 return -EINVAL;
 300
 301         if (offset + buf_len > data_len)
 302                 buf_len = data_len - offset;
 303         return sg_pcopy_to_buffer(table, sg_nents(table), buffer, buf_len,
 304                                   offset);
 305 }
 306
 307 /**
 308  * dev_coredumpm - create device coredump with read/free methods
 309  * @dev: the struct device for the crashed device
 310  * @owner: the module that contains the read/free functions, use %THIS_MODULE
 311  * @data: data cookie for the @read/@free functions
 312  * @datalen: length of the data
 313  * @gfp: allocation flags
 314  * @read: function to read from the given buffer
 315  * @free: function to free the given buffer
 316  *
 317  * Creates a new device coredump for the given device. If a previous one hasn't
 318  * been read yet, the new coredump is discarded. The data lifetime is determined
 319  * by the device coredump framework and when it is no longer needed the @free
 320  * function will be called to free the data.
 321  */
 322 void dev_coredumpm(struct device *dev, struct module *owner,
 323                    void *data, size_t datalen, gfp_t gfp,
 324                    ssize_t (*read)(char *buffer, loff_t offset, size_t count,
 325                                    void *data, size_t datalen),
 326                    void (*free)(void *data))
 327 {
 328         static atomic_t devcd_count = ATOMIC_INIT(0);
 329         struct devcd_entry *devcd;
 330         struct device *existing;
 331
 332         if (devcd_disabled)
 333                 goto free;
 334
 335         existing = class_find_device(&devcd_class, NULL, dev,
 336                                      devcd_match_failing);
 337         if (existing) {
 338                 put_device(existing);
 339                 goto free;
 340         }
 341
 342         if (!try_module_get(owner))
 343                 goto free;
 344
 345         devcd = kzalloc(sizeof(*devcd), gfp);
 346         if (!devcd)
 347                 goto put_module;
 348
 349         devcd->owner = owner;
 350         devcd->data = data;
 351         devcd->datalen = datalen;
 352         devcd->read = read;
 353         devcd->free = free;
 354         devcd->failing_dev = get_device(dev);
 355         devcd->delete_work = false;
 356
 357         mutex_init(&devcd->mutex);
 358         device_initialize(&devcd->devcd_dev);
 359
 360         dev_set_name(&devcd->devcd_dev, "devcd%d",
 361                      atomic_inc_return(&devcd_count));
 362         devcd->devcd_dev.class = &devcd_class;
 363
 364         mutex_lock(&devcd->mutex);
 365         if (device_add(&devcd->devcd_dev))
 366                 goto put_device;
 367
 368         /*
 369          * These should normally not fail, but there is no problem
 370          * continuing without the links, so just warn instead of
 371          * failing.
 372          */
 373         if (sysfs_create_link(&devcd->devcd_dev.kobj, &dev->kobj,
 374                               "failing_device") ||
 375             sysfs_create_link(&dev->kobj, &devcd->devcd_dev.kobj,
 376                               "devcoredump"))
 377                 dev_warn(dev, "devcoredump create_link failed\n");
 378
 379         INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
 380         schedule_delayed_work(&devcd->del_wk, DEVCD_TIMEOUT);
 381         mutex_unlock(&devcd->mutex);
 382         return;
 383  put_device:
 384         put_device(&devcd->devcd_dev);
 385         mutex_unlock(&devcd->mutex);
 386  put_module:
 387         module_put(owner);
 388  free:
 389         free(data);
 390 }
 391 EXPORT_SYMBOL_GPL(dev_coredumpm);
 392
 393 /**
 394  * dev_coredumpsg - create device coredump that uses scatterlist as data
 395  * parameter
 396  * @dev: the struct device for the crashed device
 397  * @table: the dump data
 398  * @datalen: length of the data
 399  * @gfp: allocation flags
 400  *
 401  * Creates a new device coredump for the given device. If a previous one hasn't
 402  * been read yet, the new coredump is discarded. The data lifetime is determined
 403  * by the device coredump framework and when it is no longer needed
 404  * it will free the data.
 405  */
 406 void dev_coredumpsg(struct device *dev, struct scatterlist *table,
 407                     size_t datalen, gfp_t gfp)
 408 {
 409         dev_coredumpm(dev, NULL, table, datalen, gfp, devcd_read_from_sgtable,
 410                       devcd_free_sgtable);
 411 }
 412 EXPORT_SYMBOL_GPL(dev_coredumpsg);
 413
 414 static int __init devcoredump_init(void)
 415 {
 416         return class_register(&devcd_class);
 417 }
 418 __initcall(devcoredump_init);
 419
 420 static void __exit devcoredump_exit(void)
 421 {
 422         class_for_each_device(&devcd_class, NULL, NULL, devcd_free);
 423         class_unregister(&devcd_class);
 424 }
 425 __exitcall(devcoredump_exit);