netdev - Re: [PATCH net-next v2 3/7] ethtool: trim policy tables

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Date:   Thu, 8 Oct 2020 11:12:02 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, kernel-team@...com,
        johannes@...solutions.net, jiri@...nulli.us, andrew@...n.ch,
        mkubecek@...e.cz
Subject: Re: [PATCH net-next v2 3/7] ethtool: trim policy tables



On 10/6/20 12:07 AM, Jakub Kicinski wrote:
> Since ethtool uses strict attribute validation there's no need
> to initialize all attributes in policy tables. 0 is NLA_UNSPEC
> which is going to be rejected. Remove the NLA_REJECTs.
> 
> Similarly attributes above maxattrs are rejected, so there's
> no need to always size the policy tables to ETHTOOL_A_..._MAX.
> 

This implies that all policy tables must be 'complete'.

strset_stringsets_policy[] for example is :

static const struct nla_policy strset_stringsets_policy[] = {
    [ETHTOOL_A_STRINGSETS_STRINGSET]    = { .type = NLA_NESTED },
};

So when later strset_parse_request() does :

req_info->counts_only = tb[ETHTOOL_A_STRSET_COUNTS_ONLY];

We have an out-of-bound access since ETHTOOL_A_STRSET_COUNTS_ONLY > ETHTOOL_A_STRINGSETS_STRINGSET

Not sure what was the expected type for this attribute, the kernel
only looks at its presence, not its value.