linux-kernel - Re: [PATCH net V2] net: bridge: br_fdb_external_learn_add(): always set EXT

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Message-ID: <56ef0a03-500a-4f0d-a231-25b1f7d58758@blackwall.org>
Date: Tue, 3 Sep 2024 11:52:05 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Jonas Gorski <jonas.gorski@...dn.de>, Roopa Prabhu <roopa@...dia.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Ido Schimmel <idosch@...lanox.com>, Petr Machata <petrm@...lanox.com>
Cc: bridge@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net V2] net: bridge: br_fdb_external_learn_add(): always
 set EXT_LEARN

On 9/3/24 11:19, Jonas Gorski wrote:
> When userspace wants to take over a fdb entry by setting it as
> EXTERN_LEARNED, we set both flags BR_FDB_ADDED_BY_EXT_LEARN and
> BR_FDB_ADDED_BY_USER in br_fdb_external_learn_add().
> 
> If the bridge updates the entry later because its port changed, we clear
> the BR_FDB_ADDED_BY_EXT_LEARN flag, but leave the BR_FDB_ADDED_BY_USER
> flag set.
> 
> If userspace then wants to take over the entry again,
> br_fdb_external_learn_add() sees that BR_FDB_ADDED_BY_USER and skips
> setting the BR_FDB_ADDED_BY_EXT_LEARN flags, thus silently ignores the
> update.
> 
> Fix this by always allowing to set BR_FDB_ADDED_BY_EXT_LEARN regardless
> if this was a user fdb entry or not.
> 
> Fixes: 710ae7287737 ("net: bridge: Mark FDB entries that were added by user as such")
> Signed-off-by: Jonas Gorski <jonas.gorski@...dn.de>
> ---
> Changelog:
> V2:
>  * always allow setting EXT_LEARN regardless if user entry
>  * reworded the commit message a bit to match the new behavior
>  * dropped the redundant code excerpt from the commit message as it's
>    already in the context
> 
>  net/bridge/br_fdb.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index c77591e63841..ad7a42b505ef 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -1469,12 +1469,10 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
>  			modified = true;
>  		}
>  
> -		if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> +		if (test_and_set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
>  			/* Refresh entry */
>  			fdb->used = jiffies;
> -		} else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> -			/* Take over SW learned entry */
> -			set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
> +		} else {
>  			modified = true;
>  		}
>  

Although the curly braces aren't needed, I don't mind in this case.

Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>