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

From: Hans Schultz <[email-masked]>
Date: Tue, 15 Mar 2022 09:48:52 +0100

On mån, mar 14, 2022 at 17:30, Ido Schimmel <[email-masked]> wrote:
> 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 <[email-masked]>
>> ---
>>  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.
>

Yes, the flag is only readable from user space, unless there is a wish
to change that.

>> +				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:
>

Yes, looks like that's more optimal. :)

> 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
>>