[PATCH 2/2] Bluetooth: HIDP: validate numbered report payloads

[Sangho Lee <kudo3228@gmail.com>]

When hidp_get_raw_report() waits for a numbered report,
hidp_process_data() compares the expected report number with skb->data[0].
A connected HIDP peer can reply with only a DATA transaction header,
leaving the skb empty after the header is removed.

KMSAN reports an uninitialized-value use in hidp_session_run(), with the
value originating in __alloc_skb() through vhci_write(). The transaction
header checks remove the empty-frame reports, but this report remains until
the payload check is added.

The comparison can also consume a peer-controlled byte beyond the declared
L2CAP PDU. A DATA | FEATURE response followed by an extra 0x01 byte made
the current code accept that byte as report ID 1 and complete
HIDIOCGFEATURE with a zero-byte result. With this change the malformed
response is rejected with -EIO, while a subsequent valid response still
succeeds.

Require a payload byte before comparing a numbered report ID. Unnumbered
reports continue to accept an empty payload.

Fixes: 0ff1731a1ae5 ("HID: bt: Add support for hidraw HIDIOCGFEATURE and HIDIOCSFEATURE")
Cc: stable@vger.kernel.org
Signed-off-by: Sangho Lee <kudo3228@gmail.com>
---
 net/bluetooth/hidp/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
index 194208d03d18..f5bdf9f1ca63 100644
--- a/net/bluetooth/hidp/core.c
+++ b/net/bluetooth/hidp/core.c
@@ -543,9 +543,10 @@ static int hidp_process_data(struct hidp_session *session, struct sk_buff *skb,
 	}
 
 	if (test_bit(HIDP_WAITING_FOR_RETURN, &session->flags) &&
-				param == session->waiting_report_type) {
+	    param == session->waiting_report_type) {
 		if (session->waiting_report_number < 0 ||
-		    session->waiting_report_number == skb->data[0]) {
+		    (skb->len &&
+		     session->waiting_report_number == skb->data[0])) {
 			/* hidp_get_raw_report() is waiting on this report. */
 			session->report_return = skb;
 			done_with_skb = 0;
-- 
2.43.0