[PATCH v3 0/2] Bluetooth: virtio_bt: harden rx against untrusted backend

Michael Bommarito
2026-04-21T17:08:59Z

Respin of the virtio_bt rx hardening patch, split per Luiz's
request on the v2 thread:

https://lore.kernel.org/linux-bluetooth/20260421151659.3326690-1-michael.bommarito@gmail.com/

v2 bundled two independent hazards in one commit and the commit
message got convoluted trying to explain them together. This v3
keeps each hazard in its own patch so the rationale for each is
self-contained.

Patch 1/2 keeps the original v1/v2 concern: virtbt_rx_work() calls
skb_put() with a used.len the device controls, with no validation
against the 1000-byte buffer we actually exposed to virtio via
sg_init_one(). Checking against skb_tailroom() is not enough
because alloc_skb() can leave more tailroom than 1000 bytes due to
slab padding. len == 0 is also accepted, which lets an empty skb
reach virtbt_rx_handle() where the pkt_type byte is then read from
uninitialized memory. 1/2 defines VIRTBT_RX_BUF_SIZE, reuses it in
alloc_skb() and sg_init_one(), and gates virtbt_rx_work() on
[1, VIRTBT_RX_BUF_SIZE] with bt_dev_err_ratelimited() on the drop
path.

Patch 2/2 closes a residual short-payload hazard found during v2
pre-send review. After 1/2 restricts used.len to [1, 1000], a
one-byte completion still reaches hci_recv_frame() with skb->len
pulled to 0. If that byte was 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 shape
exists for every packet type because none of the switch cases in
virtbt_rx_handle() checked skb->len against the per-type minimum
HCI header. 2/2 requires 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.

Both patches carry the same Fixes: 160fbcf3bfb9 and Cc: stable@
as the v2 commit, because both hazards have existed since the
driver switched to skb_put() for used.len handling.

Fresh runtime repro of the original skb_over_panic on an unpatched
tree and a clean reject log with 1/2 applied are attached in the
evidence bundle referenced from the v2 thread; no runtime change
between v2 and v3 beyond the split (the final tree after 1/2+2/2
is byte-identical to the v2 commit).

Prior public versions of this patch on linux-bluetooth:

v1: <20260418000138.1848813-1-michael.bommarito@gmail.com>
v2: <20260421151659.3326690-1-michael.bommarito@gmail.com>

Michael Bommarito (2):
Bluetooth: virtio_bt: clamp rx length before skb_put
Bluetooth: virtio_bt: validate rx pkt_type header length

drivers/bluetooth/virtio_bt.c | 39 ++++++++++++++++++++++++++++-------
1 file changed, 32 insertions(+), 7 deletions(-)

--
2.53.0