[PATCH v2] Bluetooth: btusb: validate Realtek vendor event length

btusb_recv_event_realtek() reads the event code at data[0] and the Realtek
subevent code at data[2] before deciding whether to consume a vendor event
as a coredump.

For example, the two-byte event ff 00 contains a complete vendor-event
header declaring zero parameters. The old classifier still reads a
nonexistent third byte and can misclassify the event as a coredump if the
adjacent byte is 0x34.

Require the HCI event header and first parameter to be present before
inspecting the Realtek subevent code. Short events continue through the
normal HCI receive path, which owns their protocol validation.

Fixes: 044014ce85a1 ("Bluetooth: btrtl: Add Realtek devcoredump support")
Signed-off-by: Pengpeng Hou <[email protected]>
---
Changes since v1: https://lore.kernel.org/all/[email protected]/
- clarify both fixed-offset reads and add a concrete short event
- add the requested Fixes tag
- rebase onto v7.2-rc4

 drivers/bluetooth/btusb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index 08c0a99a62c5..8f7ed469cac6 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -2782,7 +2782,9 @@ static int btusb_setup_realtek(struct hci_dev *hdev)
 
 static int btusb_recv_event_realtek(struct hci_dev *hdev, struct sk_buff *skb)
 {
-	if (skb->data[0] == HCI_VENDOR_PKT && skb->data[2] == RTK_SUB_EVENT_CODE_COREDUMP) {
+	if (skb->len >= HCI_EVENT_HDR_SIZE + 1 &&
+	    skb->data[0] == HCI_VENDOR_PKT &&
+	    skb->data[2] == RTK_SUB_EVENT_CODE_COREDUMP) {
 		struct rtk_dev_coredump_hdr hdr = {
 			.code = RTK_DEVCOREDUMP_CODE_MEMDUMP,
 		};