netdev - Re: [PATCH net] bridge: Do not send empty IFLA_AF

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Message-ID: <fdc3a288-c342-1c6d-4cf0-640bbfd44f56@blackwall.org>
Date:   Mon, 25 Jul 2022 10:43:00 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Benjamin Poirier <bpoirier@...dia.com>, netdev@...r.kernel.org
Cc:     Roopa Prabhu <roopa@...dia.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Henrik Bjoernlund <henrik.bjoernlund@...rochip.com>,
        bridge@...ts.linux-foundation.org, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net] bridge: Do not send empty IFLA_AF_SPEC attribute

On 25/07/2022 03:12, Benjamin Poirier wrote:
> After commit b6c02ef54913 ("bridge: Netlink interface fix."),
> br_fill_ifinfo() started to send an empty IFLA_AF_SPEC attribute when a
> bridge vlan dump is requested but an interface does not have any vlans
> configured.
> 
> iproute2 ignores such an empty attribute since commit b262a9becbcb
> ("bridge: Fix output with empty vlan lists") but older iproute2 versions as
> well as other utilities have their output changed by the cited kernel
> commit, resulting in failed test cases. Regardless, emitting an empty
> attribute is pointless and inefficient.
> 
> Avoid this change by canceling the attribute if no AF_SPEC data was added.
> 
> Fixes: b6c02ef54913 ("bridge: Netlink interface fix.")
> Reviewed-by: Ido Schimmel <idosch@...dia.com>
> Signed-off-by: Benjamin Poirier <bpoirier@...dia.com>
> ---
>  net/bridge/br_netlink.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index bb01776d2d88..c96509c442a5 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -589,9 +589,13 @@ static int br_fill_ifinfo(struct sk_buff *skb,
>  	}
>  
>  done:
> +	if (af) {
> +		if (nlmsg_get_pos(skb) - (void *)af > nla_attr_size(0))
> +			nla_nest_end(skb, af);
> +		else
> +			nla_nest_cancel(skb, af);
> +	}
>  
> -	if (af)
> -		nla_nest_end(skb, af);
>  	nlmsg_end(skb, nlh);
>  	return 0;
>  

br_fill_ifinfo has been a mess, at some point we have to refactor it.

Anyway, thanks for the patch:
Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>