From: Steve Rago <sar@nec-labs.com>
To: David Miller <davem@davemloft.net>
Cc: <luto@amacapital.net>, <netdev@vger.kernel.org>,
<mtk.manpages@gmail.com>, <ebiederm@xmission.com>
Subject: Re: bug in passing file descriptors
Date: Mon, 7 Oct 2013 15:17:24 -0400 [thread overview]
Message-ID: <525308C4.1030007@nec-labs.com> (raw)
In-Reply-To: <20131007.151233.2237348893254566536.davem@davemloft.net>
On 10/07/2013 03:12 PM, David Miller wrote:
> From: Steve Rago <sar@nec-labs.com>
> Date: Mon, 7 Oct 2013 15:06:02 -0400
>
>> Maybe. So a client expecting to receive x bytes of control
>> information should make sure their buffer is at least CMSG_SPACE(x)
>> bytes long instead of CMSG_LEN(x) bytes long, because you feel
>> compelled to copy the final padding from kernel space to user space?
>> Seems wrong to me. IMHO, the final padding should only come into play
>> when calculating where the next header should begin.
>
> Yes, all control messages must be aligned to, and be of a length of a
> multiple of, "sizeof(long)".
>
> This is the only correct way to program control messages.
>
Except when sizeof(long) can change and you need to maintain binary compatibility with older applications. x86 comes to
mind as a relevant example: used to be 32 bits, but is 64 now.
Steve
next prev parent reply other threads:[~2013-10-07 19:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-07 18:27 bug in passing file descriptors Steve Rago
2013-10-07 18:44 ` Andy Lutomirski
2013-10-07 19:06 ` Steve Rago
2013-10-07 19:12 ` David Miller
2013-10-07 19:17 ` Steve Rago [this message]
2013-10-07 19:42 ` David Miller
2013-10-07 20:29 ` Steve Rago
2013-10-07 21:32 ` David Miller
2013-10-07 22:55 ` Andi Kleen
2013-10-08 14:32 ` Steve Rago
2013-10-08 16:02 ` Andy Lutomirski
2013-10-08 16:18 ` Steve Rago
2013-10-08 16:41 ` Andi Kleen
2013-10-08 16:51 ` Steve Rago
2013-10-09 14:07 ` Steve Rago
2013-10-08 8:43 ` David Laight
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