[PATCH v2] Bluetooth: hci_event: validate skb length for unknown CC opcode

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

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In hci_cmd_complete_evt(), if the command complete event has an unknown
opcode, we assume the first byte of the remaining skb->data contains the
return status. However, parameter data has previously been pulled in
hci_event_func(), which may leave the skb empty. If so, using skb->data[0]
for the return status uses un-init memory.

The fix is to check skb->len before using skb->data.

Reported-by: syzbot+a9a4bedfca6aa9d7fa24@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a9a4bedfca6aa9d7fa24
Tested-by: syzbot+a9a4bedfca6aa9d7fa24@syzkaller.appspotmail.com
Fixes: afcb3369f46ed ("Bluetooth: hci_event: Fix vendor (unknown) opcode status handling")
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
---
changes in v2:
- check skb->len before accessing skb->data in hci_cmd_complete_evt(). 
- remove v1’s changes
- update commit message and Fixes tag 

Thank you for the response Luiz. I didn’t want to spam you or the ML
with another reply since you were very clear.

 net/bluetooth/hci_event.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index d790b0d4eb9a..d2ac95a824db 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4211,6 +4211,13 @@ static void hci_cmd_complete_evt(struct hci_dev *hdev, void *data,
 	}
 
 	if (i == ARRAY_SIZE(hci_cc_table)) {
+		if (!skb->len) {
+			bt_dev_err(hdev, "Unexpected cc 0x%4.4x with no status",
+				   *opcode);
+			*status = HCI_ERROR_UNSPECIFIED;
+			return;
+		}
+
 		/* Unknown opcode, assume byte 0 contains the status, so
 		 * that e.g. __hci_cmd_sync() properly returns errors
 		 * for vendor specific commands send by HCI drivers.
-- 
2.43.0