Bug#560348: xen: racy temporary files for kernel and initrd

[Ian Campbell <ijc@hellion.org.uk>]

On Wed, 2010-08-11 at 20:56 +0200, Paul Menzel wrote:
> Am Mittwoch, den 11.08.2010, 10:40 +0100 schrieb Ian Campbell: 
> > On Wed, 2010-08-11 at 00:05 +0200, Paul Menzel wrote:
> > >         $ grep vmlinuz /tmp/squeeze.cfg 
> > >         kernel = "/tmp/vmlinuz"
> > >         $ sudo xm create /tmp/squeeze.cfg
> > >         Using config file "/tmp/squeeze.cfg".
> > >         Error: Kernel image does not exist: /tmp/vmlinuz
> > > 
> > > Do you have any idea? This is with the daily Debian Installer files from
> > > [2].
> > 
> > Hrm. I assume /tmp/vmlinuz exists and is readable by the relevant user
> > etc. Do the logs in /var/log/xen tell you anything?
> 
[snip logs]

Thanks but unfortunately I am none the wiser :-(

> I took a look where `VmError` originates from. I think, it turns out to
> be in `/usr/lib/xen-3.2-1/lib/python/xen/xend/image.py`.
> 
>         if not os.path.isfile(self.kernel):
>             raise VmError('Kernel image does not exist: %s' % self.kernel)
> 
> But testing this manually works.
> 
>         $ python
>         >>> import os
>         >>> os.path.isfile("/tmp/vmlinuz")
>         True

Very strange.

It is likely that the process actually running is different to the user
you used for this test so perhaps there is something about the
permissions either on the files themselves or the /tmp directory or
something?

I presume this:
$ ls -l /tmp/{vmlinuz,initrd.gz}
        -rw-r--r-- 1 user user 17859729 2010-08-10 10:05 /tmp/initrd.gz
        -rw-r--r-- 1 user user  2351776 2010-08-10 10:05 /tmp/vmlinuz
is still true? But what about the perms on / and /tmp?

It's unlikely but I suppose I have to ask: are you using xm on a
different machine to the one running xend? (via either the XML/RPC or
SXP/RPC mechanisms).

It might be worth doing chmod root:root on the two files.

> Then I tried it with a different Linux kernel image under `/boot/` and
> this worked. So as a last attempt I copied `vmlinuz` from `/tmp/` to
> `/boot/` and now it works as expected. Very strange! Do I need to file a
> bug for this somewhere. Could you test that under Squeeze or Sid?

I tried it under squeeze and it seems fine.

# grep kernel /etc/xen/debian-x86_32p-1 
#kernel = "/boot/vmlinuz-x86_32p-xenU"
#kernel = "/boot/vmlinuz-2.6.32-5-xen-amd64"
kernel = "/tmp/vmlinuz-2.6.32-5-xen-amd64"
#kernel = "/scratch/lenny/i386/vmlinuz"
# ls -l /tmp/vmlinuz-2.6.32-5-xen-amd64 
-rw-r--r-- 1 root root 2467552 Aug 12 09:09 /tmp/vmlinuz-2.6.32-5-xen-amd64

Ian.

-- 
Ian Campbell

 That reminds me, we'll need to buy a chainsaw for the office. "In
       case of emergency, break glass"