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From: Sasha Levin <sasha.levin@oracle.com>
To: David Miller <davem@davemloft.net>
Cc: a.ryabinin@samsung.com, pablo@netfilter.org, mschmidt@redhat.com,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH] netlink: don't copy over empty attribute data
Date: Tue, 21 Oct 2014 22:19:36 -0400	[thread overview]
Message-ID: <54471438.1040907@oracle.com> (raw)
In-Reply-To: <20141021.213908.1088381802543942481.davem@davemloft.net>

On 10/21/2014 09:39 PM, David Miller wrote:
> From: Sasha Levin <sasha.levin@oracle.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@oracle.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".


Thanks,
Sasha

  reply	other threads:[~2014-10-22  2:19 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-21 20:51 [PATCH] netlink: don't copy over empty attribute data Sasha Levin
2014-10-22  1:39 ` David Miller
2014-10-22  2:19   ` Sasha Levin [this message]
2014-10-22  6:15     ` David Miller
2014-10-26 23:32       ` Sasha Levin
2014-10-27  2:03         ` David Miller
2014-10-27 14:42           ` Sasha Levin
2014-10-27 16:46             ` Andrey Ryabinin
2014-10-22  8:55 ` David Laight

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