linux-kernel - Re: [PATCH v2] sysctl: handle table->maxlen properly for proc

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Date:   Tue, 24 May 2022 10:30:01 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
Subject: Re: [PATCH v2] sysctl: handle table->maxlen properly for proc_dobool

On Tue, May 24, 2022 at 1:27 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
>
> On Sun, May 22, 2022 at 01:26:24PM +0800, Muchun Song wrote:
> > Setting ->proc_handler to proc_dobool at the same time setting ->maxlen
> > to sizeof(int) is counter-intuitive, it is easy to make mistakes.  For
> > robustness, fix it by reimplementing proc_dobool() properly.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > Cc: Luis Chamberlain <mcgrof@...nel.org>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Iurii Zaikin <yzaikin@...gle.com>
> > ---
>
> Thanks for your patch Muchun!
>
> Does this fix an actualy issue? Because the comit log suggest so.

Thanks for taking a look.

I think it is an improvement not a real bug fix. When I first use
proc_dobool in my driver, I assign sizeof(variable) to table->maxlen.
Then I found it was wrong, it should be sizeof(int) which was
counter-intuitive. So it is very easy to make mistakes. Should I add
those into the commit log?

Thanks.

> If so is there a bug which is known or a reproducer which can be
> implemented to showcase that bug?
>
> The reason I ask is that we have automatic scrapers for bug fixes,
> and I tend to prefer to avoid giving those automatic scrapers
> the idea that a patch is a fix for a kernel bug when it it is not.
> If what you are change is an optimization then your commit log should
> clarify that.
>
> If you are fixing something then you must be clear about about the
> details I mentioned. And then, if it does fix an issue, how long
> has the issue been know, what are the consequences of it? And up
> to what kernel is this issue present for?
>
>   Luis