linux-kernel - Re: devpts multiple instances feedback

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Message-ID: <20090126215542.GA20760@lst.de>
Date:	Mon, 26 Jan 2009 22:55:42 +0100
From:	Christoph Hellwig <hch@....de>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Christoph Hellwig <hch@....de>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: devpts multiple instances feedback

On Mon, Jan 05, 2009 at 01:09:40PM -0800, Sukadev Bhattiprolu wrote:
> Making the pts/ptmx node would certianly simplify the code. But we
> ended up with some of the complexity to preserve the legacy behavior.
> I believe there was some concern that the presence of a "shadow"
> ptmx node on older distros might affect rights management (eg: if
> the older distro which does not know about /dev/pts/ptmx, applied
> a security label to /dev/ptmx that label could be subverted by using
> /dev/pts/ptmx ?
> 
> That was also one of the reasons for the default 000 mode on the pts/ptmx
> device node

So just make it 000 but always created it.

> 
> |  - the 000 mode is very weird, given how the /dev/ptmx operates
> |    it doesn't really make much sense to have it different than 0666
> |    unless you want to disable ptys.
> |  - why does pts_sb_from_inode have to check s_magic, I can't see
> |    it ever used on an inode not from the devpts filesystem
> 
> If /dev/ptmx is not a symlink to pts/ptmx, we would need the s_magic
> check ? (eg: when called from devpts_new_index()). The check would
> not be needed if /dev/ptmx is always a symlink.

Ok, so it's for the /dev/ptmx node.  Just make that explicit by
passing down a paramter then.

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