linux-kernel - Re: [PATCH 4/4] ALSA: emu10k1: Cocci spatch "alloc

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Date:   Thu, 21 Sep 2017 18:39:15 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Thomas Meyer <thomas@...3r.de>
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ALSA: emu10k1: Cocci spatch "alloc_cast"

On Thu, Sep 21, 2017 at 08:33:46AM +0200, Thomas Meyer wrote:
> Remove casting the values returned by memory allocation functions like
> kmalloc, kzalloc, kmem_cache_alloc, kmem_cache_zalloc etc."
> Found by coccinelle spatch "api/alloc/alloc_cast.cocci"
> 
> Signed-off-by: Thomas Meyer <thomas@...3r.de>
> ---
> 
> diff -u -p a/sound/pci/emu10k1/emufx.c b/sound/pci/emu10k1/emufx.c
> --- a/sound/pci/emu10k1/emufx.c
> +++ b/sound/pci/emu10k1/emufx.c
> @@ -1218,7 +1218,7 @@ static int _snd_emu10k1_audigy_init_efx(
>  	if (!icode)
>  		return err;
>  
> -	icode->gpr_map = (u_int32_t __user *) kcalloc(512 + 256 + 256 + 2 * 1024,
> +	icode->gpr_map = kcalloc(512 + 256 + 256 + 2 * 1024,
>  						      sizeof(u_int32_t), GFP_KERNEL);

	And _this_ is a wonderful example of the reasons why that kind of
patches is bloody bad.  The code you've caught is very obviously smelly -
kcalloc() does *NOT* return a userland pointer.  You are whitewashing it;
a major "something weird is going on here" sign is gone (something weird
in that case is hopefully a set_fs(KERNEL_DS) somewhere nearby, and it
is asking for careful review).

	FWIW, any patches of that sort anywhere near VFS are very much not welcome.