linux-hardening - Re: [PATCH] staging: rtl8723bs: Use kcalloc() instead of kzalloc()

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Message-ID: <a5d8a5f1-432d-46f0-84fe-7b5b22ff5f32@moroto.mountain>
Date: Mon, 22 Jan 2024 09:55:11 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Erick Archer <erick.archer@....com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Franziska Naepelt <franziska.naepelt@...glemail.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Aloka Dixit <quic_alokad@...cinc.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] staging: rtl8723bs: Use kcalloc() instead of kzalloc()

On Fri, Jan 19, 2024 at 06:39:00PM +0100, Erick Archer wrote:
> As noted in the "Deprecated Interfaces, Language Features, Attributes,
> and Conventions" documentation [1], size calculations (especially
> multiplication) should not be performed in memory allocator (or similar)
> function arguments due to the risk of them overflowing. This could lead
> to values wrapping around and a smaller allocation being made than the
> caller was expecting. Using those allocations could lead to linear
> overflows of heap memory and other misbehaviors.
> 
> So, use the purpose specific kcalloc() function instead of the argument
> count * size in the kzalloc() function.
> 
> Also, it is preferred to use sizeof(*pointer) instead of sizeof(type)
> due to the type of the variable can change and one needs not change the
> former (unlike the latter).
> 
> Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/162
> Signed-off-by: Erick Archer <erick.archer@....com>

I quite often write responses to patches and then never send them.  I
wrote this response and debated sending it but in the end I decided to
send it because you have sent multiple patches.  If you had only sent
one patch then I wouldn't have bothered.

Generally, commit messages should say what the user visible effects of
a patch are.  Sometimes with these sorts of commits, it's hard to
determine the effect.  For example, Kees went through and changed dozens
or hundreds of these allocations to use safer constructs and we don't
necessarily expect him to audit all the code.  They should already have
been fine, but it's better to be safe.

However in this case obviously the patch is small and just by glancing
at it we can see that it has no effect on rutime.

But if someone is reviewing patches with "git log" instead of
"git log -p" they aren't going to see the patch. I can almost always
figure out what a commit does without looking at the commit message,
that doesn't mean that the commit messages are unnecessary.

So I really prefer if commit message say, "This commit is just to make
static checkers happy and to make the code more readable.  It has no
effect on runtime."  The commit message you wrote is way more scary than
is warranted.  Here is my proposed commit message:

"We are trying to get rid of all multiplications from allocation
functions to prevent integer overflows.  Here the multiplication is
obviously safe, but using kcalloc() is more appropriate and improves
readability.  This patch has no effect on runtime behavior."

regards,
dan carpenter