linux-kernel - Re: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow

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Message-ID: <878szma2hz.fsf@codeaurora.org>
Date:   Tue, 15 Jan 2019 07:55:36 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Willy Tarreau <w@....eu>
Cc:     Silvio Cesare <silvio.cesare@...il.com>,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow

Willy Tarreau <w@....eu> writes:

> 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: Kalle Valo <kvalo@...eaurora.org>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Greg KH <greg@...ah.com>
> Signed-off-by: Willy Tarreau <w@....eu>

I don't see any mention about which tree this should go to. Can I take
this to wireless-drivers-next?

-- 
Kalle Valo