netdev - Re: bug in passing file descriptors

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Message-ID: <5255631D.9010001@nec-labs.com>
Date:	Wed, 9 Oct 2013 10:07:25 -0400
From:	Steve Rago <sar@...-labs.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	David Miller <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: bug in passing file descriptors

On 10/08/2013 12:51 PM, Steve Rago wrote:
> On 10/08/2013 12:41 PM, Andi Kleen wrote:
>>> I just want the semantics to be consistent.  If you want Linux to
>>> always require applications that call recvmsg to provide a buffer
>>> size of CMSG_SPACE bytes long to retrieve control information, then
>>> fail the system call when the buffer is smaller.  But if you do
>>> this, you risk breaking applications that work with FreeBSD, Mac OS
>>> X, Solaris, and probably a few others.
>>
>> The primary concern is to be binary compatible with Linux.

Not to application developers, by the way.

>>
>> But not being compatible between 32bit and 64bit Linux processes on the same
>> host would seem like a serious problem to me.
>>
>>> Regardless, copying 20 bytes and telling me you copied 24 is misleading and wrong.
>>
>> The question is could it break existing Linux applications to change it?
>> And would it help with the 32/64bit compatibility?
>>
>> If not some other way to fix the compat layer would need to be found.
>>
>> -Andi
>>
>
> I'm not sure if a 64-bit process and a 32-bit process exchange file descriptors on the same system has a problem.  It
> certainly looks like the compat code does the right thing.  I can test this tonight if you want.

I tested all combinations and they work fine as far as Linux binary compatibility is concerned.

Steve

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