linux-kernel - Re: [PATCH 4/8] ASoC: change snprintf to scnprintf for possible overflow

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Message-ID: <20190115012536.GA12096@Asurada-Nvidia.nvidia.com>
Date:   Mon, 14 Jan 2019 17:25:37 -0800
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Willy Tarreau <w@....eu>
Cc:     Silvio Cesare <silvio.cesare@...il.com>,
        linux-kernel@...r.kernel.org, Timur Tabi <timur@...nel.org>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH 4/8] ASoC: change snprintf to scnprintf for possible
 overflow

On Sat, Jan 12, 2019 at 04:28:40PM +0100, Willy Tarreau wrote:
> From: Silvio Cesare <silvio.cesare@...il.com>
> 
> Change snprintf to scnprintf. There are generally two cases where using
> snprintf causes problems.
> 
> 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...)
> In this case, if snprintf would have written more characters than what the
> buffer size (SIZE) is, then size will end up larger than SIZE. In later
> uses of snprintf, SIZE - size will result in a negative number, leading
> to problems. Note that size might already be too large by using
> size = snprintf before the code reaches a case of size += snprintf.
> 
> 2) If size is ultimately used as a length parameter for a copy back to user
> space, then it will potentially allow for a buffer overflow and information
> disclosure when size is greater than SIZE. When the size is used to index
> the buffer directly, we can have memory corruption. This also means when
> size = snprintf... is used, it may also cause problems since size may become
> large.  Copying to userspace is mitigated by the HARDENED_USERCOPY kernel
> configuration.
> 
> The solution to these issues is to use scnprintf which returns the number of
> characters actually written to the buffer, so the size variable will never
> exceed SIZE.
> 
> Signed-off-by: Silvio Cesare <silvio.cesare@...il.com>

> Cc: Nicolin Chen <nicoleotsuka@...il.com>

I think you probably need to run get_maintainer.pl for the patch
and should send to Mark Brown and CC alsa-devel. And for subject,
we usually use prefix "ASoC: imx-audmux:". Otherwise,

Acked-by: Nicolin Chen <nicoleotsuka@...il.com>

Thanks