linux-kernel - Re: [PATCH 14/16] vfs: Implement mount_super

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Message-ID: <E79284E6-1011-4B25-8B85-58D3F60F60F6@zytor.com>
Date:	Wed, 20 Apr 2016 09:12:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Austin S. Hemmelgarn" <ahferroin7@...il.com>,
	"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: [PATCH 14/16] vfs: Implement mount_super_once

On April 20, 2016 4:50:53 AM PDT, "Austin S. Hemmelgarn" <ahferroin7@...il.com> wrote:
>On 2016-04-19 23:27, Eric W. Biederman wrote:
>> "H. Peter Anvin" <hpa@...or.com> writes:
>>
>>> On April 19, 2016 12:25:03 PM PDT, "H. Peter Anvin" <hpa@...or.com>
>wrote:
>>>>
>>>> Perhaps a (privileged) option to exempt from the global limit,
>then.
>>>> Something we can implement if asked for.
>>>>
>>>> However, I wouldn't be 100% that the reserved pool isn't used. 
>Someone
>>>> added it presumably for a reason.  An administrator could say it
>and
>>>> we'd have no idea.
>>>
>>> ... and if I personally was running a container-hosting system, I
>>> would *absolutely* set it to make sure the administrator could not
>get
>>> locked out.
>>
>> That is likely easier done by setting:
>> echo RIDICULOUSLY_LARGE_NUMBER > /proc/sys/kernel/pty/max
>This may protect against administrative lockout on a sane system with 
>responsible users, but it doesn't protect you from lockout due to a DoS
>
>attack, while the reserved pool does (or at least, it makes sure you
>can 
>still allocate a few PTY's even when under attack).

... or even accidental due to some runaway script.  (I may or may not have some first hand knowledge of a similar situation once in college...)
-- 
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