HID: hidraw: Fix invalid read in hidraw_ioctl

The syzbot fuzzer has reported a pair of problems in the
hidraw_ioctl() function: slab-out-of-bounds read and use-after-free
read.  An example of the first:

BUG: KASAN: slab-out-of-bounds in strlen+0x79/0x90 lib/string.c:525
Read of size 1 at addr ffff8881c8035f38 by task syz-executor.4/2833

CPU: 1 PID: 2833 Comm: syz-executor.4 Not tainted 5.3.0-rc2+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0xca/0x13e lib/dump_stack.c:113
  print_address_description+0x6a/0x32c mm/kasan/report.c:351
  __kasan_report.cold+0x1a/0x33 mm/kasan/report.c:482
  kasan_report+0xe/0x12 mm/kasan/common.c:612
  strlen+0x79/0x90 lib/string.c:525
  strlen include/linux/string.h:281 [inline]
  hidraw_ioctl+0x245/0xae0 drivers/hid/hidraw.c:446
  vfs_ioctl fs/ioctl.c:46 [inline]
  file_ioctl fs/ioctl.c:509 [inline]
  do_vfs_ioctl+0xd2d/0x1330 fs/ioctl.c:696
  ksys_ioctl+0x9b/0xc0 fs/ioctl.c:713
  __do_sys_ioctl fs/ioctl.c:720 [inline]
  __se_sys_ioctl fs/ioctl.c:718 [inline]
  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:718
  do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459829
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7a68f6dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459829
RDX: 0000000000000000 RSI: 0000000080404805 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7a68f6e6d4
R13: 00000000004c21de R14: 00000000004d5620 R15: 00000000ffffffff

The two problems have the same cause: hidraw_ioctl() fails to test
whether the device has been removed.  This patch adds the missing test.

Reported-and-tested-by: syzbot+5a6c4ec678a0c6ee84ba@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hidraw.c

@@ -370,7 +370,7 @@ static long hidraw_ioctl(struct file *file, unsigned int cmd,
 
 	mutex_lock(&minors_lock);
 	dev = hidraw_table[minor];
-	if (!dev) {
+	if (!dev || !dev->exist) {
 		ret = -ENODEV;
 		goto out;
 	}