linux-kernel - Re: [PATCH v06 05/36] uapi linux/sysctl.h: use __kernel_size_t instead of size

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Date:   Wed, 9 Aug 2017 01:34:20 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Mikko Rapeli <mikko.rapeli@....fi>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        "David S . Miller" <davem@...emloft.net>,
        Matthew Whitehead <tedheadster@...il.com>,
        Joel Scherpelz <jscherpelz@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [PATCH v06 05/36] uapi linux/sysctl.h: use __kernel_size_t
 instead of size_t

On Sun, Aug 06, 2017 at 06:43:56PM +0200, Mikko Rapeli wrote:
> Fixes userspace compilation error:
> 
> error: unknown type name ‘size_t’
> 
> Signed-off-by: Mikko Rapeli <mikko.rapeli@....fi>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: David S. Miller <davem@...emloft.net>
> ---
>  include/uapi/linux/sysctl.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
> index e13d48058b8d..35a4b8b417fe 100644
> --- a/include/uapi/linux/sysctl.h
> +++ b/include/uapi/linux/sysctl.h
> @@ -35,9 +35,9 @@ struct __sysctl_args {
>  	int __user *name;
>  	int nlen;
>  	void __user *oldval;
> -	size_t __user *oldlenp;
> +	__kernel_size_t __user *oldlenp;
>  	void __user *newval;
> -	size_t newlen;
> +	__kernel_size_t newlen;
>  	unsigned long __unused[4];
>  };

You should be extremely careful when replacing size_t with __kernel_size_t
because e.g. on x32 you have sizeof(size_t) < sizeof(__kernel_size_t).

In case of sysctl.h this replacement would be wrong.

I submitted an alternative fix for this bug some time ago, see
http://lkml.kernel.org/r/20170222230652.GA14373@altlinux.org


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