linux-kernel - Re: [Announce] Checkpoint-restore tool v0.1

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Date:	Tue, 31 Jul 2012 14:30:07 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"lwn@....net" <lwn@....net>, "criu@...nvz.org" <criu@...nvz.org>,
	"users@...nvz.org" <users@...nvz.org>,
	Containers <containers@...ts.linux-foundation.org>,
	cgroups mailinglist <cgroups@...r.kernel.org>
Subject: Re: [Announce] Checkpoint-restore tool v0.1

On Tue, Jul 31, 2012 at 12:21:58PM +0200, richard -rw- weinberger wrote:
> On Tue, Jul 31, 2012 at 12:16 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> > On Tue, Jul 31, 2012 at 12:08:22PM +0200, richard -rw- weinberger wrote:
> >> On Tue, Jul 31, 2012 at 11:54 AM, Pavel Emelyanov <xemul@...allels.com> wrote:
> >> >> Yeah, but I fear it's not that easy.
> >> >> We'd have to change crtools to work without ptrace().
> >> >
> >> > Well, this is hard. Using ptrace saved us from having many special-purpose
> >> > APIs for dumping various stuff (there will be an article about it). Thus I
> >> > don't know which way is simpler -- stop using ptrace or teach ptrece to allow
> >> > several tracers to attach to one task %)
> >>
> >> Allowing multiple tracers in a safe way is IMHO even more harder.
> >>
> >> BTW:  While reading prctl_set_mm() I noticed two things.
> >> 1.  Why isn't the return value of find_vma() verified?
> >
> > prctl_set_mm
> >         vma = find_vma(mm, addr);
> >         ...
> >         if (!vma) {
> >                 error = -EFAULT;
> >                 goto out;
> >         }
> >
> > these values are used in procfs statistics only. So I don't get
> > which verify you mean here.
> 
> If I do PR_SET_MM_START_BRK the if(!vma) will never be executed because
> there a break in case PR_SET_MM_START_BRK.

Yes, and this is done by purpose, since we need to setup _completely_
new memory map on restore procedure.

There is a minimal check for value being sane

	if (addr >= TASK_SIZE || addr < mmap_min_addr)
		return -EINVAL;

and the address belongs to mm::start_data|end_data area. But sure,
better to add checks that at least code/data areas do exist, otherwise
the proc output will not reflect the real state of memory maps.

	Cyrill
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