linux-hardening - Re: [PATCH v2] docs: deprecated.rst: Clarify open-coded arithmetic with literals

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Message-ID: <87r1dqdfyj.fsf@meer.lwn.net>
Date:   Tue, 14 Sep 2021 15:07:00 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>
Cc:     Len Baker <len.baker@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Joe Perches <joe@...ches.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] docs: deprecated.rst: Clarify open-coded arithmetic
 with literals

Len Baker <len.baker@....com> writes:

> Although using literals for size calculation in allocator arguments may
> be harmless due to compiler warnings in case of overflows, it is better
> to refactor the code to avoid the use of open-coded math idiom.
>
> So, clarify the preferred way in these cases.
>
> Suggested-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Len Baker <len.baker@....com>
> ---
> Changelog v1 -> v2
>  - Clarify the sentence by changing "keep <foo> out" with "avoid <foo>"
>    (Joe Perches).
>
>  Documentation/process/deprecated.rst | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> index 9d83b8db8874..b5a8be914178 100644
> --- a/Documentation/process/deprecated.rst
> +++ b/Documentation/process/deprecated.rst
> @@ -60,7 +60,8 @@ smaller allocation being made than the caller was expecting. Using those
>  allocations could lead to linear overflows of heap memory and other
>  misbehaviors. (One exception to this is literal values where the compiler
>  can warn if they might overflow. Though using literals for arguments as
> -suggested below is also harmless.)
> +suggested below is also harmless. So, the preferred way in these cases is
> +to refactor the code to avoid the open-coded math idiom.)

Sorry for being so slow to get to this...  honestly, though, I've been
staring at it for a bit and cannot figure out what you are trying to
communicate.  What does "math idiom" mean here?  If you are trying to
say that using literals is *not* harmless, then perhaps the first part
of the parenthetical should be taken out?

Confused...

jon