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

Michael Bommarito
2026-04-21T17:09:03Z

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