[PATCH v3 2/2] Bluetooth: virtio_bt: validate rx pkt_type header length

[Michael Bommarito <michael.bommarito@gmail.com>]

virtbt_rx_handle() reads the leading pkt_type byte from the RX skb
and forwards the remainder to hci_recv_frame() for every
event/ACL/SCO/ISO type, without checking that the remaining payload
is at least the fixed HCI header for that type.

After the preceding patch bounds the backend-supplied used.len to
[1, VIRTBT_RX_BUF_SIZE], a one-byte completion still reaches
hci_recv_frame() with skb->len already pulled to 0. If the byte
happened to be HCI_ACLDATA_PKT, the ACL-vs-ISO classification
fast-path in hci_dev_classify_pkt_type() dereferences
hci_acl_hdr(skb)->handle whenever the HCI device has an active
CIS_LINK, BIS_LINK, or PA_LINK connection, reading two bytes of
uninitialized RX-buffer data. The same hazard exists for every
packet type the driver accepts because none of the switch cases in
virtbt_rx_handle() check skb->len against the per-type minimum HCI
header size before handing the frame to the core.

After stripping pkt_type, require skb->len to cover the fixed
header size for the selected type (event 2, ACL 4, SCO 3, ISO 4)
before calling hci_recv_frame(); drop ratelimited otherwise.
Unknown pkt_type values still take the original kfree_skb() default
path.

Use bt_dev_err_ratelimited() because both the length and pkt_type
values come from an untrusted backend that can otherwise flood the
kernel log.

Fixes: 160fbcf3bfb9 ("Bluetooth: virtio_bt: Use skb_put to set length")
Cc: stable@vger.kernel.org
Cc: Soenke Huster <soenke.huster@eknoes.de>
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Assisted-by: Claude:claude-opus-4-7
---
Changes in v3:
- new patch, split out of the v2 commit per Luiz's request on
  the v2 thread so the per-pkt-type header-length check can be
  reviewed on its own

Changes in v2:
- in virtbt_rx_handle(), require skb->len to cover the fixed HCI
  header size for the selected pkt_type (event 2, ACL 4, SCO 3,
  ISO 4) before calling hci_recv_frame(); this prevents a one-byte
  HCI_ACLDATA_PKT completion from reaching
  hci_dev_classify_pkt_type() and dereferencing hci_acl_hdr(skb)
  over uninitialized RX buffer data when CIS/BIS/PA connections
  are present
- switch the error log to bt_dev_err_ratelimited() because the
  length and pkt_type values come from an untrusted backend that
  can otherwise flood the kernel log

 drivers/bluetooth/virtio_bt.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/bluetooth/virtio_bt.c b/drivers/bluetooth/virtio_bt.c
index 2c5c39356a1c..140ab55c9fc5 100644
--- a/drivers/bluetooth/virtio_bt.c
+++ b/drivers/bluetooth/virtio_bt.c
@@ -198,6 +198,7 @@ static int virtbt_shutdown_generic(struct hci_dev *hdev)
 
 static void virtbt_rx_handle(struct virtio_bluetooth *vbt, struct sk_buff *skb)
 {
+	size_t min_hdr;
 	__u8 pkt_type;
 
 	pkt_type = *((__u8 *) skb->data);
@@ -205,16 +206,32 @@ static void virtbt_rx_handle(struct virtio_bluetooth *vbt, struct sk_buff *skb)
 
 	switch (pkt_type) {
 	case HCI_EVENT_PKT:
+		min_hdr = sizeof(struct hci_event_hdr);
+		break;
 	case HCI_ACLDATA_PKT:
+		min_hdr = sizeof(struct hci_acl_hdr);
+		break;
 	case HCI_SCODATA_PKT:
+		min_hdr = sizeof(struct hci_sco_hdr);
+		break;
 	case HCI_ISODATA_PKT:
-		hci_skb_pkt_type(skb) = pkt_type;
-		hci_recv_frame(vbt->hdev, skb);
+		min_hdr = sizeof(struct hci_iso_hdr);
 		break;
 	default:
 		kfree_skb(skb);
-		break;
+		return;
 	}
+
+	if (skb->len < min_hdr) {
+		bt_dev_err_ratelimited(vbt->hdev,
+				       "rx pkt_type 0x%02x payload %u < hdr %zu\n",
+				       pkt_type, skb->len, min_hdr);
+		kfree_skb(skb);
+		return;
+	}
+
+	hci_skb_pkt_type(skb) = pkt_type;
+	hci_recv_frame(vbt->hdev, skb);
 }
 
 static void virtbt_rx_work(struct work_struct *work)
-- 
2.53.0