netdev - Re: [PATCH] netlink: don't copy over empty attribute data

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 22 Oct 2014 02:15:08 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sasha.levin@...cle.com
Cc:	a.ryabinin@...sung.com, pablo@...filter.org, mschmidt@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] netlink: don't copy over empty attribute data

From: Sasha Levin <sasha.levin@...cle.com>
Date: Tue, 21 Oct 2014 22:19:36 -0400

> On 10/21/2014 09:39 PM, David Miller wrote:
>> From: Sasha Levin <sasha.levin@...cle.com>
>> Date: Tue, 21 Oct 2014 16:51:09 -0400
>> 
>>> > netlink uses empty data to seperate different levels. However, we still
>>> > try to copy that data from a NULL ptr using memcpy, which is an undefined
>>> > behaviour.
>>> > 
>>> > Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
>> This isn't a POSIX C library, this it the Linux kernel, and as such
>> we can make sure none of our memcpy() implementations try to access
>> any bytes if the given length is NULL.
> 
> We can make *our* implementations work around that undefined behaviour if we
> want, but right now our implementations is to call GCC's builtin memcpy(),
> which follows the standards and doesn't allow you to call it with NULL 'from'
> ptr.
> 
> The fact that it doesn't die and behaves properly is just "luck".

If GCC's internal memcpy() starts accessing past 'len', I'm going
to report the bug rather than code around it.

That causes a page fault, you _can't_ do it.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html