Re: [PATCH v6 1/3] batman-adv: mcast: implement multicast packet reception and forwarding

[Simon Wunderlich <sw@simonwunderlich.de>]

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On Thursday, July 20, 2023 6:35:53 AM CEST Linus Lüssing wrote:
> [...]
> +
> +/**
> + * batadv_mcast_forw_orig_to_neigh() - get next hop neighbor to an orig
> address + * @bat_priv: the bat priv with all the soft interface information
> + * @orig_addr: the originator MAC address to search the best next hop
> router for + *
> + * Return: A neighbor node which is the best router towards the given
> originator + * address.
> + */
> +static struct batadv_neigh_node *
> +batadv_mcast_forw_orig_to_neigh(struct batadv_priv *bat_priv, u8
> *orig_addr) +{
> +	struct batadv_neigh_node *neigh_node;
> +	struct batadv_orig_node *orig_node;
> +
> +	orig_node = batadv_orig_hash_find(bat_priv, orig_addr);
> +	if (!orig_node)
> +		return NULL;
> +
> +	neigh_node = batadv_find_router(bat_priv, orig_node, NULL);
> +	batadv_orig_node_put(orig_node);
> +
> +	return neigh_node;
> +}

I was wondering if this shouldn't be a generic function rather than a multicast-specific function. It doesn't do anything multicast specific. I couldn't find something similar in other code though.

> +
> +/**
> + * batadv_mcast_forw_scrub_dests() - scrub destinations in a tracker TVLV
> + * @bat_priv: the bat priv with all the soft interface information
> + * @comp_neigh: next hop neighbor to scrub+collect destinations for
> + * @dest: start MAC entry in original skb's tracker TVLV
> + * @next_dest: start MAC entry in to be sent skb's tracker TVLV
> + * @num_dests: number of remaining destination MAC entries to iterate over
> + *
> + * This sorts destination entries into either the original batman-adv
> + * multicast packet or the skb (copy) that is going to be sent to
> comp_neigh + * next.
> + *
> + * In preparation for the next, to be (unicast) transmitted batman-adv
> multicast + * packet skb to be sent to the given neighbor node, tries to
> collect all + * originator MAC addresses that have the given neighbor node
> as their next hop + * in the to be transmitted skb (copy), which next_dest
> points into. That is we + * zero all destination entries in next_dest which
> do not have comp_neigh as + * their next hop. And zero all destination
> entries in the original skb that + * would have comp_neigh as their next
> hop (to avoid redundant transmissions and + * duplicated payload later).
> + */
> +static void
> +batadv_mcast_forw_scrub_dests(struct batadv_priv *bat_priv,
> +			      struct batadv_neigh_node *comp_neigh, u8 *dest,
> +			      u8 *next_dest, u16 num_dests)
> +{
> +	struct batadv_neigh_node *next_neigh;
> +
> +	/* skip first entry, this is what we are comparing with */
> +	eth_zero_addr(dest);
> +	dest += ETH_ALEN;
> +	next_dest += ETH_ALEN;
> +	num_dests--;
> +
> +	batadv_mcast_forw_tracker_for_each_dest(next_dest, num_dests) {
> +		if (is_zero_ether_addr(next_dest))
> +			goto scrub_next;
> +
> +		if (is_multicast_ether_addr(next_dest)) {
> +			eth_zero_addr(dest);
> +			eth_zero_addr(next_dest);
> +			goto scrub_next;
> +		}
> +
> +		next_neigh = batadv_mcast_forw_orig_to_neigh(bat_priv,
> +							     next_dest);
> +		if (!next_neigh) {
> +			eth_zero_addr(next_dest);
> +			goto scrub_next;
> +		}
> +
> +		/* Is this for our next packet to transmit? */
> +		if (batadv_compare_eth(next_neigh->addr, comp_neigh->addr))
> +			eth_zero_addr(dest);
> +		else
> +			eth_zero_addr(next_dest);
> +
> +		batadv_neigh_node_put(next_neigh);
> +scrub_next:
> +		dest += ETH_ALEN;

I've read through that multiple times now, and I don't understand why next_dest isn't getting incremented within each iteration in the same way as dest. Is this a bug or am I missing something? Might be nicer to use one counter which is increased instead of two pointeres, e.g. &dest[counter] and &next_dest[counter] or similar to avoid those kind of bugs.

> [...]
> +/**
> + * batadv_mcast_forw_tracker_tvlv_handler() - handle an mcast tracker tvlv
> + * @bat_priv: the bat priv with all the soft interface information
> + * @skb: the received batman-adv multicast packet
> + *
> + * Parses the tracker TVLV of an incoming batman-adv multicast packet and
> + * forwards the packet as indicated in this TVLV.
> + *
> + * Caller needs to set the skb network header to the start of the multicast
> + * tracker TVLV (excluding the generic TVLV header) and the skb transport
> header + * to the next byte after this multicast tracker TVLV.
> + *
> + * Caller needs to free the skb.
> + *
> + * Return: NET_RX_SUCCESS or NET_RX_DROP on success or a negative error
> + * code on failure. NET_RX_SUCCESS if the received packet is supposed to be
> + * decapsulated and forwarded to the own soft interface, NET_RX_DROP
> otherwise. + */
> +int batadv_mcast_forw_tracker_tvlv_handler(struct batadv_priv *bat_priv,
> +					   struct sk_buff *skb)
> +{
> +	return batadv_mcast_forw_packet(bat_priv, skb, false);
> +}
> diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
> index 34903df4fe93..e46ce83c516a 100644
> --- a/net/batman-adv/originator.c
> +++ b/net/batman-adv/originator.c
> @@ -942,6 +942,7 @@ struct batadv_orig_node *batadv_orig_node_new(struct
> batadv_priv *bat_priv, #ifdef CONFIG_BATMAN_ADV_MCAST
>  	orig_node->mcast_flags = BATADV_MCAST_WANT_NO_RTR4;
>  	orig_node->mcast_flags |= BATADV_MCAST_WANT_NO_RTR6;
> +	orig_node->mcast_flags |= BATADV_MCAST_HAVE_MC_PTYPE_CAPA;
>  	INIT_HLIST_NODE(&orig_node->mcast_want_all_unsnoopables_node);
>  	INIT_HLIST_NODE(&orig_node->mcast_want_all_ipv4_node);
>  	INIT_HLIST_NODE(&orig_node->mcast_want_all_ipv6_node);
> diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
> index 163cd43c4821..f1061985149f 100644
> --- a/net/batman-adv/routing.c
> +++ b/net/batman-adv/routing.c
> @@ -1270,3 +1270,73 @@ int batadv_recv_bcast_packet(struct sk_buff *skb,
>  	batadv_orig_node_put(orig_node);
>  	return ret;
>  }
> +
> +#ifdef CONFIG_BATMAN_ADV_MCAST
> +/**
> + * batadv_recv_mcast_packet() - process received batman-adv multicast
> packet + * @skb: the received batman-adv multicast packet
> + * @recv_if: interface that the skb is received on
> + *
> + * Parses the given, received batman-adv multicast packet. Depending on the
> + * contents of its TVLV forwards it and/or decapsulates it to hand it to
> the + * soft interface.
> + *
> + * Return: NET_RX_DROP if the skb is not consumed, NET_RX_SUCCESS
> otherwise. + */
> +int batadv_recv_mcast_packet(struct sk_buff *skb,
> +			     struct batadv_hard_iface *recv_if)
> +{
> +	struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
> +	struct batadv_mcast_packet *mcast_packet;
> +	int hdr_size = sizeof(*mcast_packet);
> +	unsigned char *tvlv_buff;
> +	int ret = NET_RX_DROP;
> +	u16 tvlv_buff_len;
> +
> +	if (batadv_check_unicast_packet(bat_priv, skb, hdr_size) < 0)
> +		goto free_skb;
> +
> +	/* create a copy of the skb, if needed, to modify it. */
> +	if (skb_cow(skb, ETH_HLEN) < 0)
> +		goto free_skb;
> +
> +	/* packet needs to be linearized to access the tvlv content */
> +	if (skb_linearize(skb) < 0)
> +		goto free_skb;
> +
> +	mcast_packet = (struct batadv_mcast_packet *)skb->data;
> +	if (mcast_packet->ttl-- < 2)
> +		goto free_skb;

More of a nit (since we do the same check in broadcasts), but if ttl == 0 on the incoming packet, then we will actually forward it with ttl =255 and that's a bit stupid ...

Cheers,
      Simon

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