Subject: Re: [PATCH] brcmfmac: drop Inter-Access Point Protocol packets by default

From: Stephen Hemminger <[email-masked]>
Date: Wed, 14 Mar 2018 08:08:31 -0700

On Wed, 14 Mar 2018 12:01:19 +0100
Rafał Miłecki <[email-masked]> wrote:

> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> index 19048526b4af..db6987015fb1 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
> @@ -230,6 +230,34 @@ static void brcmf_netdev_set_multicast_list(struct net_device *ndev)
>  	schedule_work(&ifp->multicast_work);
>  }
>  
> +/**
> + * brcmf_skb_is_iapp - checks if skb is an IAPP packet
> + *
> + * @skb: skb to check
> + */
> +static bool brcmf_skb_is_iapp(struct sk_buff *skb)
> +{
> +	const u8 iapp_l2_update_packet[6] __aligned(2) = {
> +		0x00, 0x01, 0xaf, 0x81, 0x01, 0x00,
> +	};
> +	unsigned char *eth_data = skb_mac_header(skb) + ETH_HLEN;
> +#if !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +	const u16 *a = (const u16 *)eth_data;
> +	const u16 *b = (const u16 *)iapp_l2_update_packet;
> +#endif
> +
> +	if (skb->len - skb->mac_len != 6 ||
> +	    !is_multicast_ether_addr(eth_hdr(skb)->h_dest))
> +		return false;
> +
> +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +	return !(((*(const u32 *)eth_data) ^ (*(const u32 *)iapp_l2_update_packet)) |
> +		 ((*(const u16 *)(eth_data + 4)) ^ (*(const u16 *)(iapp_l2_update_packet + 4))));
> +#else
> +	return !((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2]));
> +#endif
> +}
> +
>  static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
>  					   struct net_device *ndev)
>  {
> @@ -250,6 +278,12 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
>  		goto done;
>  	}
>  
> +	if (!IS_ENABLED(CONFIG_BRCMFMAC_IAPP) && brcmf_skb_is_iapp(skb)) {
> +		dev_kfree_skb(skb);
> +		ret = -EINVAL;
> +		goto done;
> +	}
> +

The usual way to handle config options in kernel is either inline
stub function or #define

#ifdef CONFIG_BRFMMAC_IAPP
static bool brcmf_skb_is_app(...) {
	real code
}
#else
#define brcmf_skb_is_app  (false)
#endif