Subject: Re: Does anyone care about a race free ptsname?
To: "Eric W. Biederman" <ebiederm@xmission.com>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>, security@debian.org,
        "security@kernel.org" <security@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "security@ubuntu.com >> security" <security@ubuntu.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Serge Hallyn <serge.hallyn@ubuntu.com>, Willy Tarreau <w@1wt.eu>,
        Aurelien Jarno <aurelien@aurel32.net>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Jann Horn <jann@thejh.net>, Greg KH <greg@kroah.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>, Florian Weimer <fw@deneb.enyo.de>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <57169B2D.6030606@zytor.com>
Date: Tue, 19 Apr 2016 13:55:09 -0700
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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