linux-kernel - Re: [PATCH] bpf: fix netfilter link comparison to handle unsigned flags

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Message-ID: <CAADnVQKZXEsN_SNg+WgOT02hdREM93zyDr=9fhgdJZYVzv2rfw@mail.gmail.com>
Date: Sun, 21 Sep 2025 19:20:37 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Haofeng Li <920484857@...com>
Cc: Quentin Monnet <qmo@...nel.org>, 13266079573@....com, 
	Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, lihaofeng@...inos.cn, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: fix netfilter link comparison to handle unsigned flags

On Sun, Sep 21, 2025 at 6:52 PM Haofeng Li <920484857@...com> wrote:
>
> Thank you for your review and feedback.
>
> >Did you actually observe an overflow producing an error when sorting,
> >here? Or did you run into some compiler warning?
>
> I did not encounter a runtime error or a compiler warning caused by this potential overflow.
> The issue was identified during code review as a potential risk,
> considering the theoretical possibility of wrap-around with unsigned subtraction,
> which prompted me to submit this patch for code robustness.
>
> >This being said, I don't mind making the code cleaner for these
> >comparisons, but we should probably treat all three attributes the same,
> >and update the rest of the function as well?
>
> Thank you for pointing this out.
> I will prepare a v2 patch that thoroughly reviews and updates the comparison
> logic for all three fields (netfilter.pf, netfilter.hooknum, and netfilter.flags),
> replacing all subtraction-based comparisons with explicit conditional checks.

Don't. We don't fix theoretical issues.