[PATCH] Bluetooth: hci_event: validate HCI event packet Parameter Total Length

[Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>]

There is a BUG: KMSAN: uninit-value in hci_cmd_complete_evt() due to a
malformed HCI event packet received from userspace.

The existing code in hci_event_packet() checks that the buffer is large
enough to contain the event header, and checks that the hdr's Event Code
is valid, but does not check the hdr's Parameter Total Length. So,
syzbot’s event packet passes through and uses the un-init values in
hci_event_func() => hci_cmd_complete_evt().

Reported-by: syzbot+a9a4bedfca6aa9d7fa24@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a9a4bedfca6aa9d7fa24
Tested-by: syzbot+a9a4bedfca6aa9d7fa24@syzkaller.appspotmail.com
Fixes: a9de9248064bf ("[Bluetooth] Switch from OGF+OCF to using only opcodes")
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
---
 net/bluetooth/hci_event.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index d790b0d4eb9a..5e1498cc04cd 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -7565,7 +7565,7 @@ void hci_event_packet(struct hci_dev *hdev, struct sk_buff *skb)
 	hci_req_complete_t req_complete = NULL;
 	hci_req_complete_skb_t req_complete_skb = NULL;
 	struct sk_buff *orig_skb = NULL;
-	u8 status = 0, event, req_evt = 0;
+	u8 status = 0, event, req_evt = 0, len;
 	u16 opcode = HCI_OP_NOP;
 
 	if (skb->len < sizeof(*hdr)) {
@@ -7585,6 +7585,13 @@ void hci_event_packet(struct hci_dev *hdev, struct sk_buff *skb)
 		goto done;
 	}
 
+	len = hdr->plen;
+	if (len != skb->len - HCI_EVENT_HDR_SIZE) {
+		bt_dev_warn(hdev, "Unexpected HCI Parameter Length 0x%2.2x",
+			    len);
+		goto done;
+	}
+
 	/* Only match event if command OGF is not for LE */
 	if (hdev->req_skb &&
 	    hci_opcode_ogf(hci_skb_opcode(hdev->req_skb)) != 0x08 &&
-- 
2.43.0