[PATCH v3] Bluetooth: btmtk: validate WMT event SKB length before struct access

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

btmtk_usb_hci_wmt_sync() casts the WMT event response SKB data to
struct btmtk_hci_wmt_evt (7 bytes) and struct btmtk_hci_wmt_evt_funcc
(9 bytes) without first checking that the SKB contains enough data.
A short firmware response causes out-of-bounds reads from SKB tailroom.

Add length validation before each struct access to prevent OOB reads
from malformed WMT event responses.

Fixes: d019930b0049 ("Bluetooth: btmtk: move btusb_mtk_hci_wmt_sync to btmtk.c")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 drivers/bluetooth/btmtk.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
index 6fb6ca274..b1a96ebae 100644
--- a/drivers/bluetooth/btmtk.c
+++ b/drivers/bluetooth/btmtk.c
@@ -695,6 +695,12 @@ static int btmtk_usb_hci_wmt_sync(struct hci_dev *hdev,
 	if (data->evt_skb == NULL)
 		goto err_free_wc;
 
+	/* Validate SKB length before accessing WMT event structs */
+	if (data->evt_skb->len < sizeof(*wmt_evt)) {
+		err = -EINVAL;
+		goto err_free_skb;
+	}
+
 	/* Parse and handle the return WMT event */
 	wmt_evt = (struct btmtk_hci_wmt_evt *)data->evt_skb->data;
 	if (wmt_evt->whdr.op != hdr->op) {
@@ -712,6 +718,10 @@ static int btmtk_usb_hci_wmt_sync(struct hci_dev *hdev,
 			status = BTMTK_WMT_PATCH_DONE;
 		break;
 	case BTMTK_WMT_FUNC_CTRL:
+		if (data->evt_skb->len < sizeof(*wmt_evt_funcc)) {
+			err = -EINVAL;
+			goto err_free_skb;
+		}
 		wmt_evt_funcc = (struct btmtk_hci_wmt_evt_funcc *)wmt_evt;
 		if (be16_to_cpu(wmt_evt_funcc->status) == 0x404)
 			status = BTMTK_WMT_ON_DONE;
-- 
2.47.3