linux-hardening - Re: [PATCH v2][next] sysctl: Avoid open coded arithmetic in memory allocator functions

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Message-ID: <YXWeAdsMRcR5tInN@casper.infradead.org>
Date:   Sun, 24 Oct 2021 18:55:13 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Len Baker <len.baker@....com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-hardening@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2][next] sysctl: Avoid open coded arithmetic in memory
 allocator functions

On Sun, Oct 24, 2021 at 11:13:28AM +0200, Len Baker wrote:
> I think it is better to be defensive. IMHO I believe that if the
> struct_size() helper could be used in this patch, it would be more
> easy to ACK. But it is not possible due to the complex memory
> layouts.

I think it's better for code to be understandable.  Your patch makes
the code less readable in the name of "security", which is a poor
justification.

> However, there are a lot of code in the kernel that uses the
> struct_size() helper for memory allocator arguments where we know
> that it don't overflow. For example:

Well, yes.  That's because struct_size() actually makes code more
readable as well as more secure.

> As a last point I would like to know the opinion of Kees and
> Gustavo since they are also working on this task.
> 
> Kees and Gustavo, what do you think?

You might want to check who was co-author on 610b15c50e86 before
discarding my opinion.