linux-kernel - Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

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Message-ID: <20160412013136.GM25498@ZenIV.linux.org.uk>
Date:	Tue, 12 Apr 2016 02:31:36 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>, security@...ian.org,
	security@...nel.org,
	"security@...ntu.com >> security" <security@...ntu.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Willy Tarreau <w@....eu>,
	Aurelien Jarno <aurelien@...el32.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jann Horn <jann@...jh.net>, Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>, Florian Weimer <fw@...eb.enyo.de>
Subject: Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated
 devpts via path lookup

On Mon, Apr 11, 2016 at 07:48:28AM -0700, H. Peter Anvin wrote:
 
> Here is an entire different approach, I don't know if it is sane or not: when *mounting* the devpts filesystem, it could automagically create the bins mount for ptmx in the parent of its mount point.  Presumably the would be a mount option to disable that behavior.
> 
> Does anyone see an obvious problem with that?

Yes.  ->mount() doesn't (and fucking *shouldn't*) know anything about the
mountpoint to be.  Not to mention that the same superblock can easily end
up being visible in many places, etc.  This is insane.