drivers/hid/uhid.c

   1 /*
   2  * User-space I/O driver support for HID subsystem
   3  * Copyright (c) 2012 David Herrmann
   4  */
   5
   6 /*
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms of the GNU General Public License as published by the Free
   9  * Software Foundation; either version 2 of the License, or (at your option)
  10  * any later version.
  11  */
  12
  13 #include <linux/atomic.h>
  14 #include <linux/compat.h>
  15 #include <linux/cred.h>
  16 #include <linux/device.h>
  17 #include <linux/fs.h>
  18 #include <linux/hid.h>
  19 #include <linux/input.h>
  20 #include <linux/miscdevice.h>
  21 #include <linux/module.h>
  22 #include <linux/mutex.h>
  23 #include <linux/poll.h>
  24 #include <linux/sched.h>
  25 #include <linux/spinlock.h>
  26 #include <linux/uhid.h>
  27 #include <linux/wait.h>
  28
  29 #define UHID_NAME       "uhid"
  30 #define UHID_BUFSIZE    32
  31
  32 struct uhid_device {
  33         struct mutex devlock;
  34
  35         /* This flag tracks whether the HID device is usable for commands from
  36          * userspace. The flag is already set before hid_add_device(), which
  37          * runs in workqueue context, to allow hid_add_device() to communicate
  38          * with userspace.
  39          * However, if hid_add_device() fails, the flag is cleared without
  40          * holding devlock.
  41          * We guarantee that if @running changes from true to false while you're
  42          * holding @devlock, it's still fine to access @hid.
  43          */
  44         bool running;
  45
  46         __u8 *rd_data;
  47         uint rd_size;
  48
  49         /* When this is NULL, userspace may use UHID_CREATE/UHID_CREATE2. */
  50         struct hid_device *hid;
  51         struct uhid_event input_buf;
  52
  53         wait_queue_head_t waitq;
  54         spinlock_t qlock;
  55         __u8 head;
  56         __u8 tail;
  57         struct uhid_event *outq[UHID_BUFSIZE];
  58
  59         /* blocking GET_REPORT support; state changes protected by qlock */
  60         struct mutex report_lock;
  61         wait_queue_head_t report_wait;
  62         bool report_running;
  63         u32 report_id;
  64         u32 report_type;
  65         struct uhid_event report_buf;
  66         struct work_struct worker;
  67 };
  68
  69 static struct miscdevice uhid_misc;
  70
  71 static void uhid_device_add_worker(struct work_struct *work)
  72 {
  73         struct uhid_device *uhid = container_of(work, struct uhid_device, worker);
  74         int ret;
  75
  76         ret = hid_add_device(uhid->hid);
  77         if (ret) {
  78                 hid_err(uhid->hid, "Cannot register HID device: error %d\n", ret);
  79
  80                 /* We used to call hid_destroy_device() here, but that's really
  81                  * messy to get right because we have to coordinate with
  82                  * concurrent writes from userspace that might be in the middle
  83                  * of using uhid->hid.
  84                  * Just leave uhid->hid as-is for now, and clean it up when
  85                  * userspace tries to close or reinitialize the uhid instance.
  86                  *
  87                  * However, we do have to clear the ->running flag and do a
  88                  * wakeup to make sure userspace knows that the device is gone.
  89                  */
  90                 uhid->running = false;
  91                 wake_up_interruptible(&uhid->report_wait);
  92         }
  93 }
  94
  95 static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
  96 {
  97         __u8 newhead;
  98
  99         newhead = (uhid->head + 1) % UHID_BUFSIZE;
 100
 101         if (newhead != uhid->tail) {
 102                 uhid->outq[uhid->head] = ev;
 103                 uhid->head = newhead;
 104                 wake_up_interruptible(&uhid->waitq);
 105         } else {
 106                 hid_warn(uhid->hid, "Output queue is full\n");
 107                 kfree(ev);
 108         }
 109 }
 110
 111 static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
 112 {
 113         unsigned long flags;
 114         struct uhid_event *ev;
 115
 116         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 117         if (!ev)
 118                 return -ENOMEM;
 119
 120         ev->type = event;
 121
 122         spin_lock_irqsave(&uhid->qlock, flags);
 123         uhid_queue(uhid, ev);
 124         spin_unlock_irqrestore(&uhid->qlock, flags);
 125
 126         return 0;
 127 }
 128
 129 static int uhid_hid_start(struct hid_device *hid)
 130 {
 131         struct uhid_device *uhid = hid->driver_data;
 132         struct uhid_event *ev;
 133         unsigned long flags;
 134
 135         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 136         if (!ev)
 137                 return -ENOMEM;
 138
 139         ev->type = UHID_START;
 140
 141         if (hid->report_enum[HID_FEATURE_REPORT].numbered)
 142                 ev->u.start.dev_flags |= UHID_DEV_NUMBERED_FEATURE_REPORTS;
 143         if (hid->report_enum[HID_OUTPUT_REPORT].numbered)
 144                 ev->u.start.dev_flags |= UHID_DEV_NUMBERED_OUTPUT_REPORTS;
 145         if (hid->report_enum[HID_INPUT_REPORT].numbered)
 146                 ev->u.start.dev_flags |= UHID_DEV_NUMBERED_INPUT_REPORTS;
 147
 148         spin_lock_irqsave(&uhid->qlock, flags);
 149         uhid_queue(uhid, ev);
 150         spin_unlock_irqrestore(&uhid->qlock, flags);
 151
 152         return 0;
 153 }
 154
 155 static void uhid_hid_stop(struct hid_device *hid)
 156 {
 157         struct uhid_device *uhid = hid->driver_data;
 158
 159         hid->claimed = 0;
 160         uhid_queue_event(uhid, UHID_STOP);
 161 }
 162
 163 static int uhid_hid_open(struct hid_device *hid)
 164 {
 165         struct uhid_device *uhid = hid->driver_data;
 166
 167         return uhid_queue_event(uhid, UHID_OPEN);
 168 }
 169
 170 static void uhid_hid_close(struct hid_device *hid)
 171 {
 172         struct uhid_device *uhid = hid->driver_data;
 173
 174         uhid_queue_event(uhid, UHID_CLOSE);
 175 }
 176
 177 static int uhid_hid_parse(struct hid_device *hid)
 178 {
 179         struct uhid_device *uhid = hid->driver_data;
 180
 181         return hid_parse_report(hid, uhid->rd_data, uhid->rd_size);
 182 }
 183
 184 /* must be called with report_lock held */
 185 static int __uhid_report_queue_and_wait(struct uhid_device *uhid,
 186                                         struct uhid_event *ev,
 187                                         __u32 *report_id)
 188 {
 189         unsigned long flags;
 190         int ret;
 191
 192         spin_lock_irqsave(&uhid->qlock, flags);
 193         *report_id = ++uhid->report_id;
 194         uhid->report_type = ev->type + 1;
 195         uhid->report_running = true;
 196         uhid_queue(uhid, ev);
 197         spin_unlock_irqrestore(&uhid->qlock, flags);
 198
 199         ret = wait_event_interruptible_timeout(uhid->report_wait,
 200                                 !uhid->report_running || !uhid->running,
 201                                 5 * HZ);
 202         if (!ret || !uhid->running || uhid->report_running)
 203                 ret = -EIO;
 204         else if (ret < 0)
 205                 ret = -ERESTARTSYS;
 206         else
 207                 ret = 0;
 208
 209         uhid->report_running = false;
 210
 211         return ret;
 212 }
 213
 214 static void uhid_report_wake_up(struct uhid_device *uhid, u32 id,
 215                                 const struct uhid_event *ev)
 216 {
 217         unsigned long flags;
 218
 219         spin_lock_irqsave(&uhid->qlock, flags);
 220
 221         /* id for old report; drop it silently */
 222         if (uhid->report_type != ev->type || uhid->report_id != id)
 223                 goto unlock;
 224         if (!uhid->report_running)
 225                 goto unlock;
 226
 227         memcpy(&uhid->report_buf, ev, sizeof(*ev));
 228         uhid->report_running = false;
 229         wake_up_interruptible(&uhid->report_wait);
 230
 231 unlock:
 232         spin_unlock_irqrestore(&uhid->qlock, flags);
 233 }
 234
 235 static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
 236                                u8 *buf, size_t count, u8 rtype)
 237 {
 238         struct uhid_device *uhid = hid->driver_data;
 239         struct uhid_get_report_reply_req *req;
 240         struct uhid_event *ev;
 241         int ret;
 242
 243         if (!uhid->running)
 244                 return -EIO;
 245
 246         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 247         if (!ev)
 248                 return -ENOMEM;
 249
 250         ev->type = UHID_GET_REPORT;
 251         ev->u.get_report.rnum = rnum;
 252         ev->u.get_report.rtype = rtype;
 253
 254         ret = mutex_lock_interruptible(&uhid->report_lock);
 255         if (ret) {
 256                 kfree(ev);
 257                 return ret;
 258         }
 259
 260         /* this _always_ takes ownership of @ev */
 261         ret = __uhid_report_queue_and_wait(uhid, ev, &ev->u.get_report.id);
 262         if (ret)
 263                 goto unlock;
 264
 265         req = &uhid->report_buf.u.get_report_reply;
 266         if (req->err) {
 267                 ret = -EIO;
 268         } else {
 269                 ret = min3(count, (size_t)req->size, (size_t)UHID_DATA_MAX);
 270                 memcpy(buf, req->data, ret);
 271         }
 272
 273 unlock:
 274         mutex_unlock(&uhid->report_lock);
 275         return ret;
 276 }
 277
 278 static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
 279                                const u8 *buf, size_t count, u8 rtype)
 280 {
 281         struct uhid_device *uhid = hid->driver_data;
 282         struct uhid_event *ev;
 283         int ret;
 284
 285         if (!uhid->running || count > UHID_DATA_MAX)
 286                 return -EIO;
 287
 288         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 289         if (!ev)
 290                 return -ENOMEM;
 291
 292         ev->type = UHID_SET_REPORT;
 293         ev->u.set_report.rnum = rnum;
 294         ev->u.set_report.rtype = rtype;
 295         ev->u.set_report.size = count;
 296         memcpy(ev->u.set_report.data, buf, count);
 297
 298         ret = mutex_lock_interruptible(&uhid->report_lock);
 299         if (ret) {
 300                 kfree(ev);
 301                 return ret;
 302         }
 303
 304         /* this _always_ takes ownership of @ev */
 305         ret = __uhid_report_queue_and_wait(uhid, ev, &ev->u.set_report.id);
 306         if (ret)
 307                 goto unlock;
 308
 309         if (uhid->report_buf.u.set_report_reply.err)
 310                 ret = -EIO;
 311         else
 312                 ret = count;
 313
 314 unlock:
 315         mutex_unlock(&uhid->report_lock);
 316         return ret;
 317 }
 318
 319 static int uhid_hid_raw_request(struct hid_device *hid, unsigned char reportnum,
 320                                 __u8 *buf, size_t len, unsigned char rtype,
 321                                 int reqtype)
 322 {
 323         u8 u_rtype;
 324
 325         switch (rtype) {
 326         case HID_FEATURE_REPORT:
 327                 u_rtype = UHID_FEATURE_REPORT;
 328                 break;
 329         case HID_OUTPUT_REPORT:
 330                 u_rtype = UHID_OUTPUT_REPORT;
 331                 break;
 332         case HID_INPUT_REPORT:
 333                 u_rtype = UHID_INPUT_REPORT;
 334                 break;
 335         default:
 336                 return -EINVAL;
 337         }
 338
 339         switch (reqtype) {
 340         case HID_REQ_GET_REPORT:
 341                 return uhid_hid_get_report(hid, reportnum, buf, len, u_rtype);
 342         case HID_REQ_SET_REPORT:
 343                 return uhid_hid_set_report(hid, reportnum, buf, len, u_rtype);
 344         default:
 345                 return -EIO;
 346         }
 347 }
 348
 349 static int uhid_hid_output_raw(struct hid_device *hid, __u8 *buf, size_t count,
 350                                unsigned char report_type)
 351 {
 352         struct uhid_device *uhid = hid->driver_data;
 353         __u8 rtype;
 354         unsigned long flags;
 355         struct uhid_event *ev;
 356
 357         switch (report_type) {
 358         case HID_FEATURE_REPORT:
 359                 rtype = UHID_FEATURE_REPORT;
 360                 break;
 361         case HID_OUTPUT_REPORT:
 362                 rtype = UHID_OUTPUT_REPORT;
 363                 break;
 364         default:
 365                 return -EINVAL;
 366         }
 367
 368         if (count < 1 || count > UHID_DATA_MAX)
 369                 return -EINVAL;
 370
 371         ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 372         if (!ev)
 373                 return -ENOMEM;
 374
 375         ev->type = UHID_OUTPUT;
 376         ev->u.output.size = count;
 377         ev->u.output.rtype = rtype;
 378         memcpy(ev->u.output.data, buf, count);
 379
 380         spin_lock_irqsave(&uhid->qlock, flags);
 381         uhid_queue(uhid, ev);
 382         spin_unlock_irqrestore(&uhid->qlock, flags);
 383
 384         return count;
 385 }
 386
 387 static int uhid_hid_output_report(struct hid_device *hid, __u8 *buf,
 388                                   size_t count)
 389 {
 390         return uhid_hid_output_raw(hid, buf, count, HID_OUTPUT_REPORT);
 391 }
 392
 393 struct hid_ll_driver uhid_hid_driver = {
 394         .start = uhid_hid_start,
 395         .stop = uhid_hid_stop,
 396         .open = uhid_hid_open,
 397         .close = uhid_hid_close,
 398         .parse = uhid_hid_parse,
 399         .raw_request = uhid_hid_raw_request,
 400         .output_report = uhid_hid_output_report,
 401         .max_buffer_size = UHID_DATA_MAX,
 402 };
 403 EXPORT_SYMBOL_GPL(uhid_hid_driver);
 404
 405 #ifdef CONFIG_COMPAT
 406
 407 /* Apparently we haven't stepped on these rakes enough times yet. */
 408 struct uhid_create_req_compat {
 409         __u8 name[128];
 410         __u8 phys[64];
 411         __u8 uniq[64];
 412
 413         compat_uptr_t rd_data;
 414         __u16 rd_size;
 415
 416         __u16 bus;
 417         __u32 vendor;
 418         __u32 product;
 419         __u32 version;
 420         __u32 country;
 421 } __attribute__((__packed__));
 422
 423 static int uhid_event_from_user(const char __user *buffer, size_t len,
 424                                 struct uhid_event *event)
 425 {
 426         if (in_compat_syscall()) {
 427                 u32 type;
 428
 429                 if (get_user(type, buffer))
 430                         return -EFAULT;
 431
 432                 if (type == UHID_CREATE) {
 433                         /*
 434                          * This is our messed up request with compat pointer.
 435                          * It is largish (more than 256 bytes) so we better
 436                          * allocate it from the heap.
 437                          */
 438                         struct uhid_create_req_compat *compat;
 439
 440                         compat = kzalloc(sizeof(*compat), GFP_KERNEL);
 441                         if (!compat)
 442                                 return -ENOMEM;
 443
 444                         buffer += sizeof(type);
 445                         len -= sizeof(type);
 446                         if (copy_from_user(compat, buffer,
 447                                            min(len, sizeof(*compat)))) {
 448                                 kfree(compat);
 449                                 return -EFAULT;
 450                         }
 451
 452                         /* Shuffle the data over to proper structure */
 453                         event->type = type;
 454
 455                         memcpy(event->u.create.name, compat->name,
 456                                 sizeof(compat->name));
 457                         memcpy(event->u.create.phys, compat->phys,
 458                                 sizeof(compat->phys));
 459                         memcpy(event->u.create.uniq, compat->uniq,
 460                                 sizeof(compat->uniq));
 461
 462                         event->u.create.rd_data = compat_ptr(compat->rd_data);
 463                         event->u.create.rd_size = compat->rd_size;
 464
 465                         event->u.create.bus = compat->bus;
 466                         event->u.create.vendor = compat->vendor;
 467                         event->u.create.product = compat->product;
 468                         event->u.create.version = compat->version;
 469                         event->u.create.country = compat->country;
 470
 471                         kfree(compat);
 472                         return 0;
 473                 }
 474                 /* All others can be copied directly */
 475         }
 476
 477         if (copy_from_user(event, buffer, min(len, sizeof(*event))))
 478                 return -EFAULT;
 479
 480         return 0;
 481 }
 482 #else
 483 static int uhid_event_from_user(const char __user *buffer, size_t len,
 484                                 struct uhid_event *event)
 485 {
 486         if (copy_from_user(event, buffer, min(len, sizeof(*event))))
 487                 return -EFAULT;
 488
 489         return 0;
 490 }
 491 #endif
 492
 493 static int uhid_dev_create2(struct uhid_device *uhid,
 494                             const struct uhid_event *ev)
 495 {
 496         struct hid_device *hid;
 497         size_t rd_size, len;
 498         void *rd_data;
 499         int ret;
 500
 501         if (uhid->hid)
 502                 return -EALREADY;
 503
 504         rd_size = ev->u.create2.rd_size;
 505         if (rd_size <= 0 || rd_size > HID_MAX_DESCRIPTOR_SIZE)
 506                 return -EINVAL;
 507
 508         rd_data = kmemdup(ev->u.create2.rd_data, rd_size, GFP_KERNEL);
 509         if (!rd_data)
 510                 return -ENOMEM;
 511
 512         uhid->rd_size = rd_size;
 513         uhid->rd_data = rd_data;
 514
 515         hid = hid_allocate_device();
 516         if (IS_ERR(hid)) {
 517                 ret = PTR_ERR(hid);
 518                 goto err_free;
 519         }
 520
 521         /* @hid is zero-initialized, strncpy() is correct, strlcpy() not */
 522         len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1;
 523         strncpy(hid->name, ev->u.create2.name, len);
 524         len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1;
 525         strncpy(hid->phys, ev->u.create2.phys, len);
 526         len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1;
 527         strncpy(hid->uniq, ev->u.create2.uniq, len);
 528
 529         hid->ll_driver = &uhid_hid_driver;
 530         hid->bus = ev->u.create2.bus;
 531         hid->vendor = ev->u.create2.vendor;
 532         hid->product = ev->u.create2.product;
 533         hid->version = ev->u.create2.version;
 534         hid->country = ev->u.create2.country;
 535         hid->driver_data = uhid;
 536         hid->dev.parent = uhid_misc.this_device;
 537
 538         uhid->hid = hid;
 539         uhid->running = true;
 540
 541         /* Adding of a HID device is done through a worker, to allow HID drivers
 542          * which use feature requests during .probe to work, without they would
 543          * be blocked on devlock, which is held by uhid_char_write.
 544          */
 545         schedule_work(&uhid->worker);
 546
 547         return 0;
 548
 549 err_free:
 550         kfree(uhid->rd_data);
 551         uhid->rd_data = NULL;
 552         uhid->rd_size = 0;
 553         return ret;
 554 }
 555
 556 static int uhid_dev_create(struct uhid_device *uhid,
 557                            struct uhid_event *ev)
 558 {
 559         struct uhid_create_req orig;
 560
 561         orig = ev->u.create;
 562
 563         if (orig.rd_size <= 0 || orig.rd_size > HID_MAX_DESCRIPTOR_SIZE)
 564                 return -EINVAL;
 565         if (copy_from_user(&ev->u.create2.rd_data, orig.rd_data, orig.rd_size))
 566                 return -EFAULT;
 567
 568         memcpy(ev->u.create2.name, orig.name, sizeof(orig.name));
 569         memcpy(ev->u.create2.phys, orig.phys, sizeof(orig.phys));
 570         memcpy(ev->u.create2.uniq, orig.uniq, sizeof(orig.uniq));
 571         ev->u.create2.rd_size = orig.rd_size;
 572         ev->u.create2.bus = orig.bus;
 573         ev->u.create2.vendor = orig.vendor;
 574         ev->u.create2.product = orig.product;
 575         ev->u.create2.version = orig.version;
 576         ev->u.create2.country = orig.country;
 577
 578         return uhid_dev_create2(uhid, ev);
 579 }
 580
 581 static int uhid_dev_destroy(struct uhid_device *uhid)
 582 {
 583         if (!uhid->hid)
 584                 return -EINVAL;
 585
 586         uhid->running = false;
 587         wake_up_interruptible(&uhid->report_wait);
 588
 589         cancel_work_sync(&uhid->worker);
 590
 591         hid_destroy_device(uhid->hid);
 592         uhid->hid = NULL;
 593         kfree(uhid->rd_data);
 594
 595         return 0;
 596 }
 597
 598 static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
 599 {
 600         if (!uhid->running)
 601                 return -EINVAL;
 602
 603         hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input.data,
 604                          min_t(size_t, ev->u.input.size, UHID_DATA_MAX), 0);
 605
 606         return 0;
 607 }
 608
 609 static int uhid_dev_input2(struct uhid_device *uhid, struct uhid_event *ev)
 610 {
 611         if (!uhid->running)
 612                 return -EINVAL;
 613
 614         hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input2.data,
 615                          min_t(size_t, ev->u.input2.size, UHID_DATA_MAX), 0);
 616
 617         return 0;
 618 }
 619
 620 static int uhid_dev_get_report_reply(struct uhid_device *uhid,
 621                                      struct uhid_event *ev)
 622 {
 623         if (!uhid->running)
 624                 return -EINVAL;
 625
 626         uhid_report_wake_up(uhid, ev->u.get_report_reply.id, ev);
 627         return 0;
 628 }
 629
 630 static int uhid_dev_set_report_reply(struct uhid_device *uhid,
 631                                      struct uhid_event *ev)
 632 {
 633         if (!uhid->running)
 634                 return -EINVAL;
 635
 636         uhid_report_wake_up(uhid, ev->u.set_report_reply.id, ev);
 637         return 0;
 638 }
 639
 640 static int uhid_char_open(struct inode *inode, struct file *file)
 641 {
 642         struct uhid_device *uhid;
 643
 644         uhid = kzalloc(sizeof(*uhid), GFP_KERNEL);
 645         if (!uhid)
 646                 return -ENOMEM;
 647
 648         mutex_init(&uhid->devlock);
 649         mutex_init(&uhid->report_lock);
 650         spin_lock_init(&uhid->qlock);
 651         init_waitqueue_head(&uhid->waitq);
 652         init_waitqueue_head(&uhid->report_wait);
 653         uhid->running = false;
 654         INIT_WORK(&uhid->worker, uhid_device_add_worker);
 655
 656         file->private_data = uhid;
 657         nonseekable_open(inode, file);
 658
 659         return 0;
 660 }
 661
 662 static int uhid_char_release(struct inode *inode, struct file *file)
 663 {
 664         struct uhid_device *uhid = file->private_data;
 665         unsigned int i;
 666
 667         uhid_dev_destroy(uhid);
 668
 669         for (i = 0; i < UHID_BUFSIZE; ++i)
 670                 kfree(uhid->outq[i]);
 671
 672         kfree(uhid);
 673
 674         return 0;
 675 }
 676
 677 static ssize_t uhid_char_read(struct file *file, char __user *buffer,
 678                                 size_t count, loff_t *ppos)
 679 {
 680         struct uhid_device *uhid = file->private_data;
 681         int ret;
 682         unsigned long flags;
 683         size_t len;
 684
 685         /* they need at least the "type" member of uhid_event */
 686         if (count < sizeof(__u32))
 687                 return -EINVAL;
 688
 689 try_again:
 690         if (file->f_flags & O_NONBLOCK) {
 691                 if (uhid->head == uhid->tail)
 692                         return -EAGAIN;
 693         } else {
 694                 ret = wait_event_interruptible(uhid->waitq,
 695                                                 uhid->head != uhid->tail);
 696                 if (ret)
 697                         return ret;
 698         }
 699
 700         ret = mutex_lock_interruptible(&uhid->devlock);
 701         if (ret)
 702                 return ret;
 703
 704         if (uhid->head == uhid->tail) {
 705                 mutex_unlock(&uhid->devlock);
 706                 goto try_again;
 707         } else {
 708                 len = min(count, sizeof(**uhid->outq));
 709                 if (copy_to_user(buffer, uhid->outq[uhid->tail], len)) {
 710                         ret = -EFAULT;
 711                 } else {
 712                         kfree(uhid->outq[uhid->tail]);
 713                         uhid->outq[uhid->tail] = NULL;
 714
 715                         spin_lock_irqsave(&uhid->qlock, flags);
 716                         uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;
 717                         spin_unlock_irqrestore(&uhid->qlock, flags);
 718                 }
 719         }
 720
 721         mutex_unlock(&uhid->devlock);
 722         return ret ? ret : len;
 723 }
 724
 725 static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
 726                                 size_t count, loff_t *ppos)
 727 {
 728         struct uhid_device *uhid = file->private_data;
 729         int ret;
 730         size_t len;
 731
 732         /* we need at least the "type" member of uhid_event */
 733         if (count < sizeof(__u32))
 734                 return -EINVAL;
 735
 736         ret = mutex_lock_interruptible(&uhid->devlock);
 737         if (ret)
 738                 return ret;
 739
 740         memset(&uhid->input_buf, 0, sizeof(uhid->input_buf));
 741         len = min(count, sizeof(uhid->input_buf));
 742
 743         ret = uhid_event_from_user(buffer, len, &uhid->input_buf);
 744         if (ret)
 745                 goto unlock;
 746
 747         switch (uhid->input_buf.type) {
 748         case UHID_CREATE:
 749                 /*
 750                  * 'struct uhid_create_req' contains a __user pointer which is
 751                  * copied from, so it's unsafe to allow this with elevated
 752                  * privileges (e.g. from a setuid binary) or via kernel_write().
 753                  */
 754                 if (file->f_cred != current_cred() || uaccess_kernel()) {
 755                         pr_err_once("UHID_CREATE from different security context by process %d (%s), this is not allowed.\n",
 756                                     task_tgid_vnr(current), current->comm);
 757                         ret = -EACCES;
 758                         goto unlock;
 759                 }
 760                 ret = uhid_dev_create(uhid, &uhid->input_buf);
 761                 break;
 762         case UHID_CREATE2:
 763                 ret = uhid_dev_create2(uhid, &uhid->input_buf);
 764                 break;
 765         case UHID_DESTROY:
 766                 ret = uhid_dev_destroy(uhid);
 767                 break;
 768         case UHID_INPUT:
 769                 ret = uhid_dev_input(uhid, &uhid->input_buf);
 770                 break;
 771         case UHID_INPUT2:
 772                 ret = uhid_dev_input2(uhid, &uhid->input_buf);
 773                 break;
 774         case UHID_GET_REPORT_REPLY:
 775                 ret = uhid_dev_get_report_reply(uhid, &uhid->input_buf);
 776                 break;
 777         case UHID_SET_REPORT_REPLY:
 778                 ret = uhid_dev_set_report_reply(uhid, &uhid->input_buf);
 779                 break;
 780         default:
 781                 ret = -EOPNOTSUPP;
 782         }
 783
 784 unlock:
 785         mutex_unlock(&uhid->devlock);
 786
 787         /* return "count" not "len" to not confuse the caller */
 788         return ret ? ret : count;
 789 }
 790
 791 static __poll_t uhid_char_poll(struct file *file, poll_table *wait)
 792 {
 793         struct uhid_device *uhid = file->private_data;
 794         __poll_t mask = EPOLLOUT | EPOLLWRNORM; /* uhid is always writable */
 795
 796         poll_wait(file, &uhid->waitq, wait);
 797
 798         if (uhid->head != uhid->tail)
 799                 mask |= EPOLLIN | EPOLLRDNORM;
 800
 801         return mask;
 802 }
 803
 804 static const struct file_operations uhid_fops = {
 805         .owner          = THIS_MODULE,
 806         .open           = uhid_char_open,
 807         .release        = uhid_char_release,
 808         .read           = uhid_char_read,
 809         .write          = uhid_char_write,
 810         .poll           = uhid_char_poll,
 811         .llseek         = no_llseek,
 812 };
 813
 814 static struct miscdevice uhid_misc = {
 815         .fops           = &uhid_fops,
 816         .minor          = UHID_MINOR,
 817         .name           = UHID_NAME,
 818 };
 819 module_misc_device(uhid_misc);
 820
 821 MODULE_LICENSE("GPL");
 822 MODULE_AUTHOR("David Herrmann <dh.herrmann@gmail.com>");
 823 MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");
 824 MODULE_ALIAS_MISCDEV(UHID_MINOR);
 825 MODULE_ALIAS("devname:" UHID_NAME);