linux-kernel - Re: [PATCH] devpts: If initialization failed, don't crash when opening /dev/ptmx

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Message-ID: <554BF418.5080200@hurleysoftware.com>
Date:	Thu, 07 May 2015 19:24:08 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Iulia Manda <iulia.manda21@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Fabian Frederick <fabf@...net.be>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] devpts: If initialization failed, don't crash when opening
 /dev/ptmx

On 05/07/2015 06:59 PM, Andrew Morton wrote:
> On Wed, 6 May 2015 17:35:47 -0700 Josh Triplett <josh@...htriplett.org> wrote:
> 
>> If devpts failed to initialize, it would store an ERR_PTR in the global
>> devpts_mnt.  A subsequent open of /dev/ptmx would call devpts_new_index,
>> which would dereference devpts_mnt and crash.
>>
>> Avoid storing invalid values in devpts_mnt; leave it NULL instead.
>> Make both devpts_new_index and devpts_pty_new fail gracefully with
>> ENODEV in that case, which then becomes the return value to the
>> userspace open call on /dev/ptmx.
> 
> It looks like the system is pretty crippled if init_devptr_fs() fails. 
> Can the user actually get access to consoles and do useful things in
> this situation?  Maybe it would be better to just give up and panic?

A single-user console is definitely reachable without devpts.
>From there, one could fixup to a not-broken kernel.

Regards,
Peter Hurley

PS - But I saw you already added these to -mm
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