linux-kernel - Re: [PATCH] x86/microcode/intel: Fix allocation size of struct ucode

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Message-ID: <20170106000237.5dybkvr35sbba2yx@pd.tnic>
Date:   Fri, 6 Jan 2017 01:02:37 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH] x86/microcode/intel: Fix allocation size of struct
 ucode_patch

On Thu, Jan 05, 2017 at 11:52:07PM +0000, Junichi Nomura wrote:
> >> +       p = kzalloc(sizeof(struct ucode_patch), GFP_KERNEL);
> > 
> > Perhaps sizeof(*p) ?
> 
> Yeah, that might be preferred.

No, those things are never preferred because

	sizeof(struct <type>)

tells you exactly the size of what kind of object you're getting vs

	sizeof(*p)

which tells you you're getting the size of what p points to.

Now you have to go look at p and what type it is. In the current case, p
is defined not far away from the use site but in a larger function, you
most likely need to eyeball up to its type when reading the code. Which
makes the whole thing less readable.

-- 
Regards/Gruss,
    Boris.

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