Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Fix broadcast packet CRC calculation

[Sven Eckelmann <sven@narfation.org>]

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On Wednesday 17 October 2012 13:38:30 Linus Lüssing wrote:
> So far the crc16 checksum for a batman-adv broadcast data packet, received
> on a batman-adv hard interface, was calculated over zero bytes of its
> content leading to many incoming broadcast data packets wrongly being
> dropped.
> 
> This patch fixes this issue by calculating the crc16 over the actual,
> complete broadcast payload.
> 
> The issue is a regrission introduced by
> e5cf86d30a9b32feccb6b866a3f23b0e0483a3b0.
> 
> Signed-off-by: Linus Lüssing <linus.luessing@web.de>
> ---
> It led to about 60-80% broadcast packet loss to a direct neighbor
> with a ping6 with a 1s interval in our scenario, but about no
> packet loss with an interval smaller than 0.2s.
> 
> Also see: https://projects.universe-factory.net/issues/65 (German)
> 
>  bridge_loop_avoidance.c |    8 ++++----
>  routing.c               |    8 +++++++-
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/bridge_loop_avoidance.c b/bridge_loop_avoidance.c
> index 6705d35..e7b5777 100644
> --- a/bridge_loop_avoidance.c
> +++ b/bridge_loop_avoidance.c
> @@ -1205,8 +1205,8 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
>  /**
>   * batadv_bla_check_bcast_duplist
>   * @bat_priv: the bat priv with all the soft interface information
> - * @bcast_packet: originator mac address
> - * @hdr_size: maximum length of the frame
> + * @bcast_packet: encapsulated broadcast frame plus batman header
> + * @bcast_packet_len: length of encapsulated broadcast frame plus batman
> header *
>   * check if it is on our broadcast list. Another gateway might
>   * have sent the same packet because it is connected to the same backbone,
> @@ -1219,14 +1219,14 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
>   */
>  int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
>  				   struct batadv_bcast_packet *bcast_packet,
> -				   int hdr_size)
> +				   int bcast_packet_len)
>  {
>  	int i, length, curr;
>  	uint8_t *content;
>  	uint16_t crc;
>  	struct batadv_bcast_duplist_entry *entry;
> 
> -	length = hdr_size - sizeof(*bcast_packet);
> +	length = bcast_packet_len - sizeof(*bcast_packet);
>  	content = (uint8_t *)bcast_packet;
>  	content += sizeof(*bcast_packet);
> 
> diff --git a/routing.c b/routing.c
> index bc2b88b..f861b7c 100644
> --- a/routing.c
> +++ b/routing.c
> @@ -1136,8 +1136,14 @@ int batadv_recv_bcast_packet(struct sk_buff *skb,
> 
>  	spin_unlock_bh(&orig_node->bcast_seqno_lock);
> 
> +	/* keep skb linear for crc calculation */
> +	if (skb_linearize(skb) < 0)
> +		goto out;
> +
> +	bcast_packet = (struct batadv_bcast_packet *)skb->data;
> +
>  	/* check whether this has been sent by another originator before */
> -	if (batadv_bla_check_bcast_duplist(bat_priv, bcast_packet, hdr_size))
> +	if (batadv_bla_check_bcast_duplist(bat_priv, bcast_packet, skb->len))
>  		goto out;
> 
>  	/* rebroadcast packet */

Btw. why should renaming the hdr_size to bcast_packet_len help to get a 
different value than 0?

Kind regards,
	Sven

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