linux-kernel - Re: [PATCH net v2] net: netfilter: Fix port selection of FTP for NF_NAT_RANGE_PROTO

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Message-ID: <4o2rqroo-orpr-1so2-4s5n-o1pn8no16553@vanv.qr>
Date:   Wed, 8 Sep 2021 08:52:49 +0200 (CEST)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Duncan Roe <duncan_roe@...usnet.com.au>
cc:     Florian Westphal <fw@...len.de>,
        Cole Dishington <Cole.Dishington@...iedtelesis.co.nz>,
        pablo@...filter.org, kadlec@...filter.org, davem@...emloft.net,
        kuba@...nel.org, shuah@...nel.org, linux-kernel@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org,
        Anthony Lineham <anthony.lineham@...iedtelesis.co.nz>,
        Scott Parlane <scott.parlane@...iedtelesis.co.nz>,
        Blair Steven <blair.steven@...iedtelesis.co.nz>
Subject: Re: [PATCH net v2] net: netfilter: Fix port selection of FTP for
 NF_NAT_RANGE_PROTO_SPECIFIED


On Wednesday 2021-09-08 04:22, Duncan Roe wrote:
>> >Either use if (nat->range_info.min_proto.all || ...
>> >
>> >or use ntohs().  I will leave it up to you if you prefer
>> >ntohs(nat->range_info.min_proto.all) == 0 or
>> >nat->range_info.min_proto.all == ntohs(0).
>>
>> If one has the option, one should always prefer to put htons/htonl on
>> the side with the constant literal;
>> Propagation of constants and compile-time evaluation is the target.
>>
>> That works for some other functions as well (e.g.
>> strlen("fixedstring")).
>
>When comparing against constant zero, why use htons/htonl at all?

Logical correctness.
Remember, it was the sparse tool that complained in the first place.