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

From: Kalle Valo <kvalo@codeaurora.org>
To: Willy Tarreau <w@1wt.eu>
Cc: Silvio Cesare <silvio.cesare@gmail.com>,
	linux-kernel@vger.kernel.org,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Kees Cook <keescook@chromium.org>,
	Will Deacon <will.deacon@arm.com>, Greg KH <greg@kroah.com>
Subject: Re: [PATCH 2/8] libertas: change snprintf to scnprintf for possible overflow
Date: Wed, 16 Jan 2019 18:40:29 +0200	[thread overview]
Message-ID: <87a7k04kua.fsf@codeaurora.org> (raw)
In-Reply-To: <20190115203503.GA7117@1wt.eu> (Willy Tarreau's message of "Tue, 15 Jan 2019 21:35:03 +0100")

Willy Tarreau <w@1wt.eu> writes:

> On Tue, Jan 15, 2019 at 07:55:36AM +0200, Kalle Valo wrote:
>> Willy Tarreau <w@1wt.eu> writes:
>> 
>> > From: Silvio Cesare <silvio.cesare@gmail.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@gmail.com>
>> > Cc: Kalle Valo <kvalo@codeaurora.org>
>> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
>> > Cc: Kees Cook <keescook@chromium.org>
>> > Cc: Will Deacon <will.deacon@arm.com>
>> > Cc: Greg KH <greg@kroah.com>
>> > Signed-off-by: Willy Tarreau <w@1wt.eu>
>> 
>> I don't see any mention about which tree this should go to. Can I take
>> this to wireless-drivers-next?
>
> Possibly. It addresses a small memory disclosure issue when using debugfs,
> and as such it should probably also be submitted to stable branches, so
> please use the most suitable tree that doesn't add too much extra delay.

Ok, I'll queue this for 5.0 and apply it to wireless-drivers instead.

-- 
Kalle Valo