Re: [RFCv2 5/6] Bluetooth: Correct packet len calculation

[Marcel Holtmann <marcel@holtmann.org>]

Hi Andrei,

> Remove unneeded skb_pull and correct packet length calculation
> removing magic number.
> ---
>  net/bluetooth/hci_event.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index cfccf7e..21c1bf0 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -2268,8 +2268,6 @@ static inline void hci_num_comp_pkts_evt(struct hci_dev *hdev, struct sk_buff *s
>  	struct hci_ev_num_comp_pkts *ev = (void *) skb->data;
>  	int i;
>  
> -	skb_pull(skb, sizeof(*ev));
> -
>  	BT_DBG("%s num_hndl %d", hdev->name, ev->num_hndl);
>  
>  	if (hdev->flow_ctl_mode != HCI_FLOW_CTL_MODE_PACKET_BASED) {
> @@ -2277,7 +2275,8 @@ static inline void hci_num_comp_pkts_evt(struct hci_dev *hdev, struct sk_buff *s
>  		return;
>  	}
>  
> -	if (skb->len < ev->num_hndl * 4) {
> +	if (skb->len < ev->num_hndl * sizeof(struct hci_comp_pkts_info) +
> +			sizeof(*ev)) {
>  		BT_DBG("%s bad parameters", hdev->name);
>  		return;
>  	}

actually this check is not enough. You need to make this two-fold.

	if (skb->len < sizeof(*ev)) {
		...
		return;
	}

This needs to be checked first. Otherwise you are accessing ev->num_hndl
before even knowing that it is valid. A malicious device could otherwise
sneak in some weird behavior.

Regards

Marcel