linux-kernel - Re: [PATCH] devpts: Make each mount of devpts an independent filesystem.

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Date:	Tue, 19 Apr 2016 21:49:52 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	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: [PATCH] devpts: Make each mount of devpts an independent filesystem.

On Tue, Apr 19, 2016 at 9:36 PM, Konstantin Khlebnikov <koct9i@...il.com> wrote:
> On Wed, Apr 20, 2016 at 6:04 AM, Eric W. Biederman
>>
>> The kernel.pty.reserve sysctl is neutered with no way currently
>> implemented to be able to use the reserved ptys.
>
> I think we could convert this into reserve for init user namespace,
> ssh in host will work even if containers eaten all ptys.

Yes. That's basically how it effectively worked before (ie everything
but the initial non-newinstance devpts mount would be limited to the
non-reserved numbers).

We required the non-init namespaces to do a newinstance mount, so the
whole test for "newinstance" was effectively the same thing as just
checking for the init namespace from a security standpoint.

And in fact, rewriting it in that form (ie checking for init_ns) would
just make it much more obvious what the intent it.

              Linus