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

[Nicolin Chen]

On Sat, Jan 12, 2019 at 04:28:40PM +0100, Willy Tarreau wrote:
> From: Silvio Cesare <silvio.cesare@xxxxxxxxx>
> 
> 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@xxxxxxxxx>

> Cc: Nicolin Chen <nicoleotsuka@xxxxxxxxx>

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@xxxxxxxxx>

Thanks