netdev - Re: [RFC PATCH v2 2/3] netlink: implement nla

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Date:	Thu, 2 Dec 2010 05:20:37 -0500
From:	Thomas Graf <tgraf@...radead.org>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [RFC PATCH v2 2/3] netlink: implement nla_policy for HW QOS

On Wed, Dec 01, 2010 at 10:22:58AM -0800, John Fastabend wrote:
> +
> +		NLA_PUT_U8(skb, IFLA_TC_TXMAX, dev->max_tcs);
> +		NLA_PUT_U8(skb, IFLA_TC_TXNUM, dev->num_tcs);
> +
> +		tc_txq = nla_nest_start(skb, IFLA_TC_TXQS);

You have to check the return value here.

> +		for (i = 0; i < dev->num_tcs; i++) {
> +			tcq = netdev_get_tc_queue(dev, i);
> +			ifla_tcq.tc = i;
> +			ifla_tcq.count = tcq->count;
> +			ifla_tcq.offset = tcq->offset;
> +
> +			NLA_PUT(skb, IFLA_TC_TXQ, sizeof(ifla_tcq), &ifla_tcq);
> +		}
> +		nla_nest_end(skb, tc_txq);
> +
> +		tc_map = nla_nest_start(skb, IFLA_TC_MAPS);

Same here

> +		for (i = 0; i < 16; i++) {
> +			ifla_map.prio = i;
> +			ifla_map.tc = netdev_get_prio_tc_map(dev, i);
> +			NLA_PUT(skb, IFLA_TC_MAP, sizeof(ifla_map), &ifla_map);
> +		}
>  
> +
> +static const struct nla_policy ifla_tc_txq[IFLA_TC_TXQS_MAX+1] = {
> +	[IFLA_TC_TXQ]		= { .type = NLA_BINARY,
> +				    .len = sizeof(struct ifla_tc_txq)},

This is probably not what you want. NLA_BINARY only enforces a maximum
payload length but no minimum payload length.

Omit the .type and let it fall back to NLA_UNSPEC and only specify a
.len. This enforces that the attribute payload is at least .len in
length. You should not worry about payload that exceeds your size
expectations. This allows to extend ifla_tc_txq in the future.

> +static const struct nla_policy ifla_tc_map[IFLA_TC_MAPS_MAX+1] = {
> +	[IFLA_TC_MAP]		= { .type = NLA_BINARY,
> +				    .len = sizeof(struct ifla_tc_map)},
> +};

Same here
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