Re: [PATCH net-next 1/3] net: bridge: add fdb flag to extent locked port feature

[Ido Schimmel <idosch@idosch.org>]

On Thu, Mar 10, 2022 at 03:23:18PM +0100, Hans Schultz wrote:
> Add an intermediate state for clients behind a locked port to allow for
> possible opening of the port for said clients. This feature corresponds
> to the Mac-Auth and MAC Authentication Bypass (MAB) named features. The
> latter defined by Cisco.
> 
> Signed-off-by: Hans Schultz <schultz.hans+netdev@gmail.com>
> ---
>  include/uapi/linux/neighbour.h |  1 +
>  net/bridge/br_fdb.c            |  6 ++++++
>  net/bridge/br_input.c          | 11 ++++++++++-
>  net/bridge/br_private.h        |  3 ++-
>  4 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/neighbour.h b/include/uapi/linux/neighbour.h
> index db05fb55055e..83115a592d58 100644
> --- a/include/uapi/linux/neighbour.h
> +++ b/include/uapi/linux/neighbour.h
> @@ -208,6 +208,7 @@ enum {
>  	NFEA_UNSPEC,
>  	NFEA_ACTIVITY_NOTIFY,
>  	NFEA_DONT_REFRESH,
> +	NFEA_LOCKED,
>  	__NFEA_MAX
>  };
>  #define NFEA_MAX (__NFEA_MAX - 1)
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 6ccda68bd473..396dcf3084cf 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -105,6 +105,7 @@ static int fdb_fill_info(struct sk_buff *skb, const struct net_bridge *br,
>  	struct nda_cacheinfo ci;
>  	struct nlmsghdr *nlh;
>  	struct ndmsg *ndm;
> +	u8 ext_flags = 0;
>  
>  	nlh = nlmsg_put(skb, portid, seq, type, sizeof(*ndm), flags);
>  	if (nlh == NULL)
> @@ -125,11 +126,16 @@ static int fdb_fill_info(struct sk_buff *skb, const struct net_bridge *br,
>  		ndm->ndm_flags |= NTF_EXT_LEARNED;
>  	if (test_bit(BR_FDB_STICKY, &fdb->flags))
>  		ndm->ndm_flags |= NTF_STICKY;
> +	if (test_bit(BR_FDB_ENTRY_LOCKED, &fdb->flags))
> +		ext_flags |= 1 << NFEA_LOCKED;
>  
>  	if (nla_put(skb, NDA_LLADDR, ETH_ALEN, &fdb->key.addr))
>  		goto nla_put_failure;
>  	if (nla_put_u32(skb, NDA_MASTER, br->dev->ifindex))
>  		goto nla_put_failure;
> +	if (nla_put_u8(skb, NDA_FDB_EXT_ATTRS, ext_flags))
> +		goto nla_put_failure;
> +
>  	ci.ndm_used	 = jiffies_to_clock_t(now - fdb->used);
>  	ci.ndm_confirmed = 0;
>  	ci.ndm_updated	 = jiffies_to_clock_t(now - fdb->updated);
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index e0c13fcc50ed..897908484b18 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -75,6 +75,7 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>  	struct net_bridge_mcast *brmctx;
>  	struct net_bridge_vlan *vlan;
>  	struct net_bridge *br;
> +	unsigned long flags = 0;
>  	u16 vid = 0;
>  	u8 state;
>  
> @@ -94,8 +95,16 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>  			br_fdb_find_rcu(br, eth_hdr(skb)->h_source, vid);
>  
>  		if (!fdb_src || READ_ONCE(fdb_src->dst) != p ||
> -		    test_bit(BR_FDB_LOCAL, &fdb_src->flags))
> +		    test_bit(BR_FDB_LOCAL, &fdb_src->flags)) {
> +			if (!fdb_src) {
> +				set_bit(BR_FDB_ENTRY_LOCKED, &flags);

This flag is read-only for user space, right? That is, the kernel needs
to reject it during netlink policy validation.

> +				br_fdb_update(br, p, eth_hdr(skb)->h_source, vid, flags);
> +			}
>  			goto drop;
> +		} else {

IIUC, we get here in case there is a non-local FDB entry with the SA
that points to our port. Can you write it as:

if (!fdb_src || READ_ONCE(fdb_src->dst) != p ||
    test_bit(BR_FDB_LOCAL, &fdb_src->flags) ||
    test_bit(BR_FDB_ENTRY_LOCKED, &fdb_src->flags)) {
    	if (!fdb_src) {
	...
	}
	goto drop;
}

> +			if (test_bit(BR_FDB_ENTRY_LOCKED, &fdb_src->flags))
> +				goto drop;
> +		}
>  	}
>  
>  	nbp_switchdev_frame_mark(p, skb);
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 48bc61ebc211..f5a0b68c4857 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -248,7 +248,8 @@ enum {
>  	BR_FDB_ADDED_BY_EXT_LEARN,
>  	BR_FDB_OFFLOADED,
>  	BR_FDB_NOTIFY,
> -	BR_FDB_NOTIFY_INACTIVE
> +	BR_FDB_NOTIFY_INACTIVE,
> +	BR_FDB_ENTRY_LOCKED,
>  };
>  
>  struct net_bridge_fdb_key {
> -- 
> 2.30.2
>