Both vhci_get_user and vhci_release race with open_timeout work. They
both contain cancel_delayed_work_sync, but do not test whether the
work actually created hdev or not. Since the work can be in progress
and _sync will wait for finishing it, we can have data->hdev allocated
when cancel_delayed_work_sync returns. But the call sites do 'if
(data->hdev)' *before* cancel_delayed_work_sync.

As a result:
* vhci_get_user allocates a second hdev and puts it into
  data->hdev. The former is leaked.
* vhci_release does not release data->hdev properly as it thinks there
  is none.

Fix both cases by moving the actual test *after* the call to
cancel_delayed_work_sync.

This can be hit by this program:
	#include <err.h>
	#include <fcntl.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <time.h>
	#include <unistd.h>

	#include <sys/stat.h>
	#include <sys/types.h>

	int main(int argc, char **argv)
	{
		int fd;

		srand(time(NULL));

		while (1) {
			const int delta = (rand() % 200 - 100) * 100;

			fd = open("/dev/vhci", O_RDWR);
			if (fd < 0)
				err(1, "open");

			usleep(1000000 + delta);

			close(fd);
		}

		return 0;
	}

And the result is:
BUG: KASAN: use-after-free in skb_queue_tail+0x13e/0x150 at addr ffff88006b0c1228
Read of size 8 by task kworker/u13:1/32068
=============================================================================
BUG kmalloc-192 (Tainted: G            E     ): kasan: bad access detected
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: Allocated in vhci_open+0x50/0x330 [hci_vhci] age=260 cpu=3 pid=32040
...
	kmem_cache_alloc_trace+0x150/0x190
	vhci_open+0x50/0x330 [hci_vhci]
	misc_open+0x35b/0x4e0
	chrdev_open+0x23b/0x510
...
INFO: Freed in vhci_release+0xa4/0xd0 [hci_vhci] age=9 cpu=2 pid=32040
...
	__slab_free+0x204/0x310
	vhci_release+0xa4/0xd0 [hci_vhci]
...
INFO: Slab 0xffffea0001ac3000 objects=16 used=13 fp=0xffff88006b0c1e00 flags=0x5fffff80004080
INFO: Object 0xffff88006b0c1200 @offset=4608 fp=0xffff88006b0c0600
Bytes b4 ffff88006b0c11f0: 09 df 00 00 01 00 00 00 00 00 00 00 00 00 00 00  ................
Object ffff88006b0c1200: 00 06 0c 6b 00 88 ff ff 00 00 00 00 00 00 00 00  ...k............
Object ffff88006b0c1210: 10 12 0c 6b 00 88 ff ff 10 12 0c 6b 00 88 ff ff  ...k.......k....
Object ffff88006b0c1220: c0 46 c2 6b 00 88 ff ff c0 46 c2 6b 00 88 ff ff  .F.k.....F.k....
Object ffff88006b0c1230: 01 00 00 00 01 00 00 00 e0 ff ff ff 0f 00 00 00  ................
Object ffff88006b0c1240: 40 12 0c 6b 00 88 ff ff 40 12 0c 6b 00 88 ff ff  @..k....@..k....
Object ffff88006b0c1250: 50 0d 6e a0 ff ff ff ff 00 02 00 00 00 00 ad de  P.n.............
Object ffff88006b0c1260: 00 00 00 00 00 00 00 00 ab 62 02 00 01 00 00 00  .........b......
Object ffff88006b0c1270: 90 b9 19 81 ff ff ff ff 38 12 0c 6b 00 88 ff ff  ........8..k....
Object ffff88006b0c1280: 03 00 20 00 ff ff ff ff ff ff ff ff 00 00 00 00  .. .............
Object ffff88006b0c1290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
Object ffff88006b0c12a0: 00 00 00 00 00 00 00 00 00 80 cd 3d 00 88 ff ff  ...........=....
Object ffff88006b0c12b0: 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00  . ..............
Redzone ffff88006b0c12c0: bb bb bb bb bb bb bb bb                          ........
Padding ffff88006b0c13f8: 00 00 00 00 00 00 00 00                          ........
CPU: 3 PID: 32068 Comm: kworker/u13:1 Tainted: G    B       E      4.4.6-0-default #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
Workqueue: hci0 hci_cmd_work [bluetooth]
 00000000ffffffff ffffffff81926cfa ffff88006be37c68 ffff88006bc27180
 ffff88006b0c1200 ffff88006b0c1234 ffffffff81577993 ffffffff82489320
 ffff88006bc24240 0000000000000046 ffff88006a100000 000000026e51eb80
Call Trace:
...
 [<ffffffff81ec8ebe>] ? skb_queue_tail+0x13e/0x150
 [<ffffffffa06e027c>] ? vhci_send_frame+0xac/0x100 [hci_vhci]
 [<ffffffffa0c61268>] ? hci_send_frame+0x188/0x320 [bluetooth]
 [<ffffffffa0c61515>] ? hci_cmd_work+0x115/0x310 [bluetooth]
 [<ffffffff811a1375>] ? process_one_work+0x815/0x1340
 [<ffffffff811a1f85>] ? worker_thread+0xe5/0x11f0
 [<ffffffff811a1ea0>] ? process_one_work+0x1340/0x1340
 [<ffffffff811b3c68>] ? kthread+0x1c8/0x230
...
Memory state around the buggy address:
 ffff88006b0c1100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88006b0c1180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88006b0c1200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88006b0c1280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88006b0c1300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

Fixes: 23424c0d (Bluetooth: Add support creating virtual AMP controllers)
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: stable 3.13+ <stable@vger.kernel.org>