netdev - Re: [PATCH net-next 3/6] net: bridge: break if __br_mdb

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Date:   Thu, 18 May 2017 16:45:32 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com,
        "David S. Miller" <davem@...emloft.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "moderated list:ETHERNET BRIDGE" <bridge@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 3/6] net: bridge: break if __br_mdb_del fails

On 5/18/17 12:27 AM, Vivien Didelot wrote:
> Be symmetric with br_mdb_add and break if __br_mdb_del returns an error.
> 
> Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
> ---
>   net/bridge/br_mdb.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
> index d20a01622b20..24eeeefb4179 100644
> --- a/net/bridge/br_mdb.c
> +++ b/net/bridge/br_mdb.c
> @@ -688,8 +688,9 @@ static int br_mdb_del(struct sk_buff *skb, struct nlmsghdr *nlh,
>   		list_for_each_entry(v, &vg->vlan_list, vlist) {
>   			entry->vid = v->vid;
>   			err = __br_mdb_del(br, entry);
> -			if (!err)
> -				__br_mdb_notify(dev, p, entry, RTM_DELMDB);
> +			if (err)
> +				break;
> +			__br_mdb_notify(dev, p, entry, RTM_DELMDB);
>   		}
>   	} else {
>   		err = __br_mdb_del(br, entry);
> 

This can potentially break user-space scripts that rely on the best-effort
behaviour, this is the normal "delete without vid & enabled vlan filtering".
You can check the fdb delete code which does the same, this was intentional.

You can add an mdb entry without a vid to all vlans, add a vlan and then try
to remove it from all vlans where it is present - with this patch obviously
that will fail at the new vlan.