From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eugene Syromiatnikov <esyr@redhat.com>
Subject: Re: [PATCH net-next v7 28/28] net: WireGuard secure network tunnel
Date: Sat, 6 Oct 2018 21:43:48 +0200
Message-ID: <20181006194348.GK32759@asgard.redhat.com>
References: <20181006025709.4019-1-Jason@zx2c4.com>
 <20181006025709.4019-29-Jason@zx2c4.com>
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Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        davem@davemloft.net, gregkh@linuxfoundation.org
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
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On Sat, Oct 06, 2018 at 04:57:09AM +0200, Jason A. Donenfeld wrote:
> +static int get_allowedips(void *ctx, const u8 *ip, u8 cidr, int family)
> +{
> +	struct allowedips_ctx *actx = ctx;
> +	struct nlattr *allowedip_nest;
> +
> +	allowedip_nest = nla_nest_start(actx->skb, actx->i++);

Second parameter of nl_nest_start is an attribute type; (ab)using it as
array index leads to special handling of such structures in parsers.
It's better to have some type like WGDEVICE_A_PEER_ITEM and provide an
additional attribute inside it for index (WGPEER_A_INDEX?).
See, for example, commit v4.12-rc1~119^2~131 ("nbd: add a status netlink
command").

> +static int get_peer(struct wireguard_peer *peer, unsigned int index,
> +		    struct allowedips_cursor *rt_cursor, struct sk_buff *skb)
> +{
> +	struct nlattr *allowedips_nest, *peer_nest = nla_nest_start(skb, index);

Same here.