linux-kernel - Re: PATCH? fix unshare(NEWPID) && vfork()

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Date:	Tue, 20 Aug 2013 12:13:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Brad Spengler <spender@...ecurity.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Colin Walters <walters@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: PATCH? fix unshare(NEWPID) && vfork()

On Tue, Aug 20, 2013 at 12:05 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 08/20, Andy Lutomirski wrote:
>>
>> On Tue, Aug 20, 2013 at 11:50 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>> >
>> >> Currently (with or without your patch), vfork() followed by
>> >> unshare(CLONE_NEWUSER) or unshare(CLONE_NEWPID) will unshare the VM.
>> >
>> > Could you spell please?
>> >
>> > We never unshare the VM. CLONE_VM in sys_unshare() paths just means
>> > "fail unless ->mm is not shared".
>> >
>>
>> Argh.  In that case this is probably buggy,
>
> I don't think so. Just we can't really unshare ->mm or implement
> unshare(CLONE_THREAD). We simply pretend it works if there is nothing
> to unshare.
>
>> sys_unshare will see CLONE_NEWPID or CLONE_NEWUSER and set
>> CLONE_THREAD.  Then it will see CLONE_THREAD and set CLONE_VM.
>
> This matches copy_process() to some degree... but looks confusing,
> I agree.

Huh?  Doesn't this mean that unshare(CLONE_NEWPID); vfork() will work
with your patches, but vfork(); unshare(CLONE_NEWPID) will fail?  (I
admit I haven't tested it.)

--Andy
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