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