Bluetooth: mgmt: Fix slab-out-of-bounds in tlv_data_is_valid

This fixes parsing of LTV entries when the length is 0.

Found with:

tools/mgmt-tester -s "Add Advertising - Success (ScRsp only)"

Add Advertising - Success (ScRsp only) - run
  Sending Add Advertising (0x003e)
  Test condition added, total 1
[   11.004577] ==================================================================
[   11.005292] BUG: KASAN: slab-out-of-bounds in tlv_data_is_valid+0x87/0xe0
[   11.005984] Read of size 1 at addr ffff888002c695b0 by task mgmt-tester/87
[   11.006711]
[   11.007176]
[   11.007429] Allocated by task 87:
[   11.008151]
[   11.008438] The buggy address belongs to the object at ffff888002c69580
[   11.008438]  which belongs to the cache kmalloc-64 of size 64
[   11.010526] The buggy address is located 48 bytes inside of
[   11.010526]  64-byte region [ffff888002c69580, ffff888002c695c0)
[   11.012423] The buggy address belongs to the page:
[   11.013291]
[   11.013544] Memory state around the buggy address:
[   11.014359]  ffff888002c69480: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[   11.015453]  ffff888002c69500: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[   11.016232] >ffff888002c69580: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
[   11.017010]                                      ^
[   11.017547]  ffff888002c69600: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
[   11.018296]  ffff888002c69680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[   11.019116] ==================================================================

Fixes: 2bb36870e8 ("Bluetooth: Unify advertising instance flags check")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/mgmt.c

@@ -7590,6 +7590,9 @@ static bool tlv_data_is_valid(struct hci_dev *hdev, u32 adv_flags, u8 *data,
 	for (i = 0, cur_len = 0; i < len; i += (cur_len + 1)) {
 		cur_len = data[i];
 
+		if (!cur_len)
+			continue;
+
 		if (data[i + 1] == EIR_FLAGS &&
 		    (!is_adv_data || flags_managed(adv_flags)))
 			return false;