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Re: [Xen-devel] [PATCH for-4.5] tools/pygrub: Fix TOCTOU race introduced by c/s 63dcc68

On 29/10/14 16:03, Olaf Hering wrote:
> On Wed, Oct 29, Andrew Cooper wrote:
>> In addition, use os.makedirs() which will also create intermediate 
>> directories
>> if they don't exist.
> Can this happen in practice, given that /var/run/xen is created by the
> runlevel scripts already? The mkdir is now really just @XEN_RUN_DIR@/pygrub.
> Olaf

Yes, although I presume not given the runlevel scripts.

XenServer, and Xapi in particular, is very different from an upstream xl
based system.  It has traditionally had its own initscripts.  We are in
the process of disentangling these, but it is not a trivial amount of work.

The result is that I have positively proved that XenServer hit this race
during automatic testing.  I agree that it shouldn't happen in reality
for a system configured as expected, but that fact alone doesn't
invalidate the fix itself.


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