linux-kernel - Re: Does anyone care about a race free ptsname?

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Date:	Tue, 19 Apr 2016 13:55:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>, security@...ian.org,
	"security@...nel.org" <security@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"security@...ntu.com >> security" <security@...ntu.com>,
	Peter Hurley <peter@...leysoftware.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: Does anyone care about a race free ptsname?

On 04/19/2016 01:32 PM, Eric W. Biederman wrote:
> 
> The challenge came in operations such as granpt.  Where you are passed
> in a ptmx file descriptor from who knows where, and you pass it on
> to applications such as pt_chown which run with elevatated privileged.
> 
> As the information is available of where devpts is mounted in
> relationship to /dev/ptmx I have no more concerns about implementing
> ptsname.  Path pased is also sufficiently backwards compatible it would
> not usually be wrong even on existing kernels.
> 

pt_chown is evil.  It should have been removed ages ago, and from the
very beginning have failed if run on a devpts filesystem.  Unfortunately
the glibc people didn't do so, and that is a major reason we're in the
current mess.

That being said, the ioctl(TIOCOPENSLAVE) idea would deal with that.

	-hpa