netdev - Re: [PATCH net-next] af_unix: dont send SCM

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Date:	Mon, 19 Sep 2011 17:02:04 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	tim.c.chen@...ux.intel.com, zheng.z.yan@...el.com,
	yanzheng@...n.com, netdev@...r.kernel.org, sfr@...b.auug.org.au,
	jirislaby@...il.com, sedat.dilek@...il.com, alex.shi@...el.com,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH net-next] af_unix: dont send SCM_CREDENTIALS by default

Le lundi 19 septembre 2011 à 06:28 +0200, Eric Dumazet a écrit :
> Le dimanche 18 septembre 2011 à 21:07 -0400, David Miller a écrit :
> > Eric, please respin your patches against current net-next, thanks!
> 
> Sure, here it is :
> 
> Its a bit different, so I didnt add Tim 'Acked-by'
> 
> [PATCH net-next] af_unix: dont send SCM_CREDENTIALS by default
> 
> Since commit 7361c36c5224 (af_unix: Allow credentials to work across
> user and pid namespaces) af_unix performance dropped a lot.
> 
> This is because we now take a reference on pid and cred in each write(),
> and release them in read(), usually done from another process,
> eventually from another cpu. This triggers false sharing.

> This patch includes SCM_CREDENTIALS information in a af_unix message/skb
> only if requested by the sender, [man 7 unix for details how to include
> ancillary data using sendmsg() system call]
> 
> Note: This might break buggy applications that expected SCM_CREDENTIAL
> from an unaware write() system call.


I appears udevd is such an application.

I am trying testing SOCK_PASSCRED flag and include SCM_CREDENTIALS if
set.



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