Re: [PATCH maint v5 3/3] batman-adv: mcast: fix duplicate mcast packets from BLA backbone to mesh

[Simon Wunderlich <sw@simonwunderlich.de>]

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On Monday, September 14, 2020 9:53:47 PM CEST Linus Lüssing wrote:
> Scenario:
> * Multicast frame send from BLA backbone gateways (multiple nodes
>   with their bat0 bridged together, with BLA enabled) sharing the same
>   LAN to nodes in the mesh
> 
> Issue:
> * Nodes receive the frame multiple times on bat0 from the mesh,
>   once from each foreign BLA backbone gateway which shares the same LAN
>   with another
> 
> For multicast frames via batman-adv broadcast packets coming from the
> same BLA backbone but from different backbone gateways duplicates are
> currently detected via a CRC history of previously received packets.
> 
> However this CRC so far was not performed for multicast frames received
> via batman-adv unicast packets. Fixing this by appyling the same check
> for such packets, too.
> 
> Room for improvements in the future: Ideally we would introduce the
> possibility to not only claim a client, but a complete originator, too.
> This would allow us to only send a multicast-in-unicast packet from a BLA
> backbone gateway claiming the node and by that avoid potential redundant
> transmissions in the first place.
> 
> Fixes: e5cf86d30a9b ("batman-adv: add broadcast duplicate check")
> Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
> ---
>  net/batman-adv/bridge_loop_avoidance.c | 107 +++++++++++++++++++++----
>  1 file changed, 92 insertions(+), 15 deletions(-)
> 
> diff --git a/net/batman-adv/bridge_loop_avoidance.c
> b/net/batman-adv/bridge_loop_avoidance.c index 3d2a66f2..e4f66dd8 100644
> --- a/net/batman-adv/bridge_loop_avoidance.c
> +++ b/net/batman-adv/bridge_loop_avoidance.c
> @@ -1580,13 +1580,16 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
>  }
> 
>  /**
> - * batadv_bla_check_bcast_duplist() - Check if a frame is in the broadcast
> dup. + * batadv_bla_check_duplist() - Check if a frame is in the broadcast
> dup. * @bat_priv: the bat priv with all the soft interface information - *
> @skb: contains the bcast_packet to be checked
> + * @skb: contains the multicast packet to be checked
> + * @payload_ptr: pointer to position inside the head buffer of the skb
> + *  marking the start of the data to be CRC'ed
> + * @orig: originator mac address, NULL if unknown
>   *
> - * check if it is on our broadcast list. Another gateway might
> - * have sent the same packet because it is connected to the same backbone,
> - * so we have to remove this duplicate.
> + * Check if it is on our broadcast list. Another gateway might have sent
> the + * same packet because it is connected to the same backbone, so we
> have to + * remove this duplicate.
>   *
>   * This is performed by checking the CRC, which will tell us
>   * with a good chance that it is the same packet. If it is furthermore
> @@ -1595,23 +1598,23 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
>   *
>   * Return: true if a packet is in the duplicate list, false otherwise.
>   */
> -bool batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
> -				    struct sk_buff *skb)
> +static bool batadv_bla_check_duplist(struct batadv_priv *bat_priv,
> +				     struct sk_buff *skb, u8 *payload_ptr,
> +				     const u8 *orig)
>  {
> +	struct batadv_bcast_duplist_entry *entry;
> +	bool ret = false;
>  	int i, curr;
>  	__be32 crc;
> -	struct batadv_bcast_packet *bcast_packet;
> -	struct batadv_bcast_duplist_entry *entry;
> -	bool ret = false;
> -
> -	bcast_packet = (struct batadv_bcast_packet *)skb->data;
> 
>  	/* calculate the crc ... */
> -	crc = batadv_skb_crc32(skb, (u8 *)(bcast_packet + 1));
> +	crc = batadv_skb_crc32(skb, payload_ptr);
> 
>  	spin_lock_bh(&bat_priv->bla.bcast_duplist_lock);
> 
>  	for (i = 0; i < BATADV_DUPLIST_SIZE; i++) {
> +		bool is_from_same_orig = false;
> +
>  		curr = (bat_priv->bla.bcast_duplist_curr + i);
>  		curr %= BATADV_DUPLIST_SIZE;
>  		entry = &bat_priv->bla.bcast_duplist[curr];
> @@ -1626,7 +1629,24 @@ bool batadv_bla_check_bcast_duplist(struct
> batadv_priv *bat_priv, if (entry->crc != crc)
>  			continue;
> 
> -		if (batadv_compare_eth(entry->orig, bcast_packet->orig))
> +		/* are the originators both known and not anonymous? */
> +		if (orig && !is_zero_ether_addr(orig) &&
> +		    !is_zero_ether_addr(entry->orig)) {
> +			/* if known, check if the new frame came from
> +			 * the same originator
> +			 */
> +			if (batadv_compare_eth(entry->orig, orig))
> +				is_from_same_orig = true;
> +		}
> +
> +		/* we are safe to take identical frames from the
> +		 * same orig, if known, as multiplications in
> +		 * the mesh are detected via the (orig, seqno) pair;
> +		 * so we can be a bit more liberal here and allow
> +		 * identical frames from the same orig which the source
> +		 * host might have sent multiple times on purpose
> +		 */
> +		if (is_from_same_orig)
>  			continue;
> 

I think this "is_from_same_orig" variable is redundant, it's not used again so 
you could continue directly above.

The rest looks good.

Cheers,
      Simon


>  		/* this entry seems to match: same crc, not too old,
> @@ -1643,7 +1663,14 @@ bool batadv_bla_check_bcast_duplist(struct
> batadv_priv *bat_priv, entry = &bat_priv->bla.bcast_duplist[curr];
>  	entry->crc = crc;
>  	entry->entrytime = jiffies;
> -	ether_addr_copy(entry->orig, bcast_packet->orig);
> +
> +	/* known originator */
> +	if (orig)
> +		ether_addr_copy(entry->orig, orig);
> +	/* anonymous originator */
> +	else
> +		eth_zero_addr(entry->orig);
> +
>  	bat_priv->bla.bcast_duplist_curr = curr;
> 
>  out:
> @@ -1652,6 +1679,48 @@ bool batadv_bla_check_bcast_duplist(struct
> batadv_priv *bat_priv, return ret;
>  }
> 
> +/**
> + * batadv_bla_check_ucast_duplist() - Check if a frame is in the broadcast
> dup. + * @bat_priv: the bat priv with all the soft interface information +
> * @skb: contains the multicast packet to be checked, decapsulated from a +
> *  unicast_packet
> + *
> + * Check if it is on our broadcast list. Another gateway might have sent
> the + * same packet because it is connected to the same backbone, so we
> have to + * remove this duplicate.
> + *
> + * Return: true if a packet is in the duplicate list, false otherwise.
> + */
> +static bool batadv_bla_check_ucast_duplist(struct batadv_priv *bat_priv,
> +					   struct sk_buff *skb)
> +{
> +	return batadv_bla_check_duplist(bat_priv, skb, (u8 *)skb->data, NULL);
> +}
> +
> +/**
> + * batadv_bla_check_bcast_duplist() - Check if a frame is in the broadcast
> dup. + * @bat_priv: the bat priv with all the soft interface information +
> * @skb: contains the bcast_packet to be checked
> + *
> + * Check if it is on our broadcast list. Another gateway might have sent
> the + * same packet because it is connected to the same backbone, so we
> have to + * remove this duplicate.
> + *
> + * Return: true if a packet is in the duplicate list, false otherwise.
> + */
> +bool batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
> +				    struct sk_buff *skb)
> +{
> +	struct batadv_bcast_packet *bcast_packet;
> +	u8 *payload_ptr;
> +
> +	bcast_packet = (struct batadv_bcast_packet *)skb->data;
> +	payload_ptr = (u8 *)(bcast_packet + 1);
> +
> +	return batadv_bla_check_duplist(bat_priv, skb, payload_ptr,
> +					bcast_packet->orig);
> +}
> +
>  /**
>   * batadv_bla_is_backbone_gw_orig() - Check if the originator is a gateway
> for *  the VLAN identified by vid.
> @@ -1866,6 +1935,14 @@ bool batadv_bla_rx(struct batadv_priv *bat_priv,
> struct sk_buff *skb, packet_type == BATADV_UNICAST)
>  				goto handled;
> 
> +	/* potential duplicates from foreign BLA backbone gateways via
> +	 * multicast-in-unicast packets
> +	 */
> +	if (is_multicast_ether_addr(ethhdr->h_dest) &&
> +	    packet_type == BATADV_UNICAST &&
> +	    batadv_bla_check_ucast_duplist(bat_priv, skb))
> +		goto handled;
> +
>  	ether_addr_copy(search_claim.addr, ethhdr->h_source);
>  	search_claim.vid = vid;
>  	claim = batadv_claim_hash_find(bat_priv, &search_claim);


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