Bluetooth: btusb: avoid NULL pointer dereference in skb_dequeue()

A NULL pointer dereference can occur in skb_dequeue() when processing a
QCA firmware crash dump on WCN7851 (0489:e0f3).

[ 93.672166] Bluetooth: hci0: ACL memdump size(589824)

[ 93.672475] BUG: kernel NULL pointer dereference, address: 0000000000000008
[ 93.672517] Workqueue: hci0 hci_devcd_rx [bluetooth]
[ 93.672598] RIP: 0010:skb_dequeue+0x50/0x80

The issue stems from handle_dump_pkt_qca() returning 0 even when a dump
packet is successfully processed. This is because it incorrectly
forwards the return value of hci_devcd_init() (which returns 0 on
success). As a result, the caller (btusb_recv_acl_qca() or
btusb_recv_evt_qca()) assumes the packet was not handled and passes it
to hci_recv_frame(), leading to premature kfree() of the skb.

Later, hci_devcd_rx() attempts to dequeue the same skb from the dump
queue, resulting in a NULL pointer dereference.

Fix this by:
1. Making handle_dump_pkt_qca() return 0 on success and negative errno
   on failure, consistent with kernel conventions.
2. Splitting dump packet detection into separate functions for ACL
   and event packets for better structure and readability.

This ensures dump packets are properly identified and consumed, avoiding
double handling and preventing NULL pointer access.

Fixes: 20981ce ("Bluetooth: btusb: Add WCN6855 devcoredump support")
Signed-off-by: En-Wei Wu <en-wei.wu@canonical.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: rickywu0421

drivers/bluetooth/btusb.c

@@ -3010,22 +3010,16 @@ static void btusb_coredump_qca(struct hci_dev *hdev)
 		bt_dev_err(hdev, "%s: triggle crash failed (%d)", __func__, err);
 }
 
-/*
- * ==0: not a dump pkt.
- * < 0: fails to handle a dump pkt
- * > 0: otherwise.
- */
+/* Return: 0 on success, negative errno on failure. */
 static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
 {
-	int ret = 1;
+	int ret = 0;
 	u8 pkt_type;
 	u8 *sk_ptr;
 	unsigned int sk_len;
 	u16 seqno;
 	u32 dump_size;
 
-	struct hci_event_hdr *event_hdr;
-	struct hci_acl_hdr *acl_hdr;
 	struct qca_dump_hdr *dump_hdr;
 	struct btusb_data *btdata = hci_get_drvdata(hdev);
 	struct usb_device *udev = btdata->udev;
@@ -3035,30 +3029,14 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
 	sk_len = skb->len;
 
 	if (pkt_type == HCI_ACLDATA_PKT) {
-		acl_hdr = hci_acl_hdr(skb);
-		if (le16_to_cpu(acl_hdr->handle) != QCA_MEMDUMP_ACL_HANDLE)
-			return 0;
 		sk_ptr += HCI_ACL_HDR_SIZE;
 		sk_len -= HCI_ACL_HDR_SIZE;
-		event_hdr = (struct hci_event_hdr *)sk_ptr;
-	} else {
-		event_hdr = hci_event_hdr(skb);
 	}
 
-	if ((event_hdr->evt != HCI_VENDOR_PKT)
-		|| (event_hdr->plen != (sk_len - HCI_EVENT_HDR_SIZE)))
-		return 0;
-
 	sk_ptr += HCI_EVENT_HDR_SIZE;
 	sk_len -= HCI_EVENT_HDR_SIZE;
 
 	dump_hdr = (struct qca_dump_hdr *)sk_ptr;
-	if ((sk_len < offsetof(struct qca_dump_hdr, data))
-		|| (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS)
-	    || (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
-		return 0;
-
-	/*it is dump pkt now*/
 	seqno = le16_to_cpu(dump_hdr->seqno);
 	if (seqno == 0) {
 		set_bit(BTUSB_HW_SSR_ACTIVE, &btdata->flags);
@@ -3132,17 +3110,84 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
 	return ret;
 }
 
+/* Return: true if the ACL packet is a dump packet, false otherwise. */
+static bool acl_pkt_is_dump_qca(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	u8 *sk_ptr;
+	unsigned int sk_len;
+
+	struct hci_event_hdr *event_hdr;
+	struct hci_acl_hdr *acl_hdr;
+	struct qca_dump_hdr *dump_hdr;
+
+	sk_ptr = skb->data;
+	sk_len = skb->len;
+
+	acl_hdr = hci_acl_hdr(skb);
+	if (le16_to_cpu(acl_hdr->handle) != QCA_MEMDUMP_ACL_HANDLE)
+		return false;
+
+	sk_ptr += HCI_ACL_HDR_SIZE;
+	sk_len -= HCI_ACL_HDR_SIZE;
+	event_hdr = (struct hci_event_hdr *)sk_ptr;
+
+	if ((event_hdr->evt != HCI_VENDOR_PKT) ||
+	    (event_hdr->plen != (sk_len - HCI_EVENT_HDR_SIZE)))
+		return false;
+
+	sk_ptr += HCI_EVENT_HDR_SIZE;
+	sk_len -= HCI_EVENT_HDR_SIZE;
+
+	dump_hdr = (struct qca_dump_hdr *)sk_ptr;
+	if ((sk_len < offsetof(struct qca_dump_hdr, data)) ||
+	    (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
+	    (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
+		return false;
+
+	return true;
+}
+
+/* Return: true if the event packet is a dump packet, false otherwise. */
+static bool evt_pkt_is_dump_qca(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	u8 *sk_ptr;
+	unsigned int sk_len;
+
+	struct hci_event_hdr *event_hdr;
+	struct qca_dump_hdr *dump_hdr;
+
+	sk_ptr = skb->data;
+	sk_len = skb->len;
+
+	event_hdr = hci_event_hdr(skb);
+
+	if ((event_hdr->evt != HCI_VENDOR_PKT)
+	    || (event_hdr->plen != (sk_len - HCI_EVENT_HDR_SIZE)))
+		return false;
+
+	sk_ptr += HCI_EVENT_HDR_SIZE;
+	sk_len -= HCI_EVENT_HDR_SIZE;
+
+	dump_hdr = (struct qca_dump_hdr *)sk_ptr;
+	if ((sk_len < offsetof(struct qca_dump_hdr, data)) ||
+	    (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
+	    (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
+		return false;
+
+	return true;
+}
+
 static int btusb_recv_acl_qca(struct hci_dev *hdev, struct sk_buff *skb)
 {
-	if (handle_dump_pkt_qca(hdev, skb))
-		return 0;
+	if (acl_pkt_is_dump_qca(hdev, skb))
+		return handle_dump_pkt_qca(hdev, skb);
 	return hci_recv_frame(hdev, skb);
 }
 
 static int btusb_recv_evt_qca(struct hci_dev *hdev, struct sk_buff *skb)
 {
-	if (handle_dump_pkt_qca(hdev, skb))
-		return 0;
+	if (evt_pkt_is_dump_qca(hdev, skb))
+		return handle_dump_pkt_qca(hdev, skb);
 	return hci_recv_frame(hdev, skb);
 }