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SubjectRe: chroot in swsusp userland interface (was: Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Date
Hi,

On Saturday 04 February 2006 21:15, Pavel Machek wrote:
}-- snip --{
> > > Index: suspend.c
> > > ===================================================================
> > > RCS file: /cvsroot/suspend/suspend/suspend.c,v
> > > retrieving revision 1.5
> > > diff -u -u -r1.5 suspend.c
> > > --- suspend.c 3 Feb 2006 22:39:24 -0000 1.5
> > > +++ suspend.c 4 Feb 2006 19:19:51 -0000
> > > @@ -360,6 +360,12 @@
> > > goto Close;
> > > }
> > > go_to_console();
> > > + /*
> > > + * From now on, system is frozen; any filesystem access may mean data corruption.
> > > + * Prevent accidental filesystem accesses by chrooting somewhere where little
> > > + * damage can be done.
> > > + */
> > > + chroot("/sys/power");
> >
> > This won't be enough if /sys/power is on a frozen ext2 and the suspending
> > utility calls open("file", O_CREAT) "by accident".
>
> ...well, we rely on sysfs files to work... at least for
> suspend-to-RAM, ok, no argument here. I doubt anyone really does mount
> anything but sysfs on /sys...
>
> > I think we should do as Olivier said: Mount tmpfs with limited size somewhere
> > and chroot to it (IMO this won't affect the underlying filesystem). Then, create
> > device files for the console and vt on it and open them from there. This should
> > be 100% safe.
>
> Looks unneccessarily complex to me. We'd have to umount that tmpfs,
> and playing with mounts inside system suspend seems wrong to me.
>
> Perhaps we can chroot into /proc... almost everyone has /proc
> mounted, right?
>
> Is it possible to move console/vt open before freeze?

No, because freeze sets the active vt for us. How about that: mount the
tmpfs before freeze, put there what we'll need, open device files from
there instead of /dev, and chroot() after atomic_snapshot? Then, after
resume we won't be chrooted and we'll be able to unmount the tmpfs
safely.

Greetings,
Rafael
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