linux-kernel - Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

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Message-ID: <5025FA5A.4090403@parallels.com>
Date:	Sat, 11 Aug 2012 10:23:22 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>
CC:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
> On 08/10/2012 12:28 PM, Alan Cox wrote:
>> Explicitly for Linux yes - this is not generally true of the AF_UNIX
>> socket domain and even the permissions aspect isn't guaranteed to be
>> supported on some BSD environments !
> 
> Yes, but let's worry about what the Linux behavior should be.
> 
>> The name is however just a proxy for the socket itself. You don't even
>> get a device node in the usual sense or the same inode in the file system
>> space.
> 
> 
> No, but it is looked up the same way any other inode is (the difference
> between FIFOs and sockets is that sockets have separate connections,
> which is also why open() on sockets would be nice.)
> 
> However, there is a fundamental difference between AF_UNIX sockets and
> open(), and that is how the pathname is delivered.  It thus would make
> more sense to provide the openat()-like information in struct
> sockaddr_un, but that may be very hard to do in a sensible way.  In that
> sense it perhaps would be cleaner to be able to do an open[at]() on the
> socket node with O_PATH (perhaps there should be an O_SOCKET option,
> even?) and pass the resulting file descriptor to bind() or connect().

I vote for this (openat + O_WHATEVER on a unix socket) as well. It will 
help us in checkpoint-restore, making handling of overmounted/unlinked
sockets much cleaner.

> 	-hpa

Thanks,
Pavel

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