linux-kernel - Re: [PATCH net v1 1/2] netlink: let len field used to parse type-not-care nested attrs

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Message-ID: <20230731120326.6bdd5bf9@kernel.org>
Date:   Mon, 31 Jul 2023 12:03:26 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lin Ma <linma@....edu.cn>
Cc:     davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        fw@...len.de, yang.lee@...ux.alibaba.com, jgg@...pe.ca,
        markzhang@...dia.com, phaddad@...dia.com, yuancan@...wei.com,
        ohartoov@...dia.com, chenzhongjin@...wei.com, aharonl@...dia.com,
        leon@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net v1 1/2] netlink: let len field used to parse
 type-not-care nested attrs

On Mon, 31 Jul 2023 20:12:47 +0800 Lin Ma wrote:
> In short, the very direct idea to fix such lengh-check-forgotten bug is
> add nla_len() checks like
> 
>   if (nla_len(nla) < SOME_LEN)
>     return -EINVAL;
> 
> However, this is tedious and just like Leon said: add another layer of
> cabal knowledge. The better solution should leverage the nla_policy and
> discard nlattr whose length is invalid when doing parsing. That is, we
> should defined a nested_policy for the X above like

Hard no. Putting array index into attr type is an advanced case and the
parsing code has to be able to deal with low level netlink details.
Higher level API should remove the nla_for_each_nested() completely
which is rather hard to achieve here.

Nacked-by: Jakub Kicinski <kuba@...nel.org>