netdev - Re: [PATCH 1/2] Revert "af_unix: dont send SCM_CREDENTIAL when dest socket is NULL"

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Date:	Thu, 04 Apr 2013 03:22:07 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	dingtianhong <dingtianhong@...wei.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Sven Joachim <svenjoac@....de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Karel Srot <ksrot@...hat.com>, <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 1/2] Revert "af_unix: dont send SCM_CREDENTIAL when dest socket is NULL"

dingtianhong <dingtianhong@...wei.com> writes:

> On 2013/4/4 10:13, Eric W. Biederman wrote:
>> 
>> This reverts commit 14134f6584212d585b310ce95428014b653dfaf6.
>> 
>> The problem that the above patch was meant to address is that af_unix
>> messages are not being coallesced because we are sending unnecesarry
>> credentials.  Not sending credentials in maybe_add_creds totally
>> breaks unconnected unix domain sockets that wish to send credentails
>> to other sockets.
>> 
>
> thanks for check the question and make a fix solution, but I still doubt that if unconnected unix
> domain socket wish to send credentails to oher sockets, why dont set
> SOCK_PASSCRED on sock->flags, I think the user need to decide the param
> and shouldnt send creds by default way.

The big issue is the semantics are the receiver sets SOCK_PASSCRED when
they want to receive credentials.  When transmitting packets from
unconnected or unaccepted sockets we don't know if the receiver has set
SOCK_PASSCRED so when in doubt transmit. Historically we always
tranmitted credentials.

Furthermore we have a real regression in udev that breaks systems, so
this patch must be reverted.

Eric
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