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SubjectRe: [PATCH] firmware: vpd: Fix section enabled flag on vpd_section_destroy
On Mon, Jul 23, 2018 at 10:23:05AM -0700, Dmitry Torokhov wrote:
> On Mon, Jul 23, 2018 at 10:13:36AM -0700, Guenter Roeck wrote:
> > On Mon, Jul 23, 2018 at 07:48:57PM +0300, Anton Vasilyev wrote:
> > > static struct ro_vpd and rw_vpd are initialized by vpd_sections_init()
> > > in vpd_probe() based on header's ro and rw sizes.
> > > In vpd_remove() vpd_section_destroy() performs deinitialization based
> > > on enabled flag, which is set to true by vpd_sections_init().
> > > This leads to call of vpd_section_destroy() on already destroyed section
> > > for probe-release-probe-release sequence if first probe performs
> > > ro_vpd initialization and second probe does not initialize it.
> > >
> >
> > I am not sure if the situation described can be seen in the first place.
> > The second probe would only not perform ro_vpd initialization if it fails
> > prior to that, ie if it fails to allocate memory or if there is a
> > consistency problem. In that case the remove function would not be called.
> >
> > However, there is a problem in the code: A partially failed probe will
> > leave the system in inconsistent state. Example: ro section initializes,
> > rw section fails to initialize. The probe will fail, but the ro section
> > will not be destroyed, its sysfs attributes still exist, and its memory
> > is still mapped. It would make more sense to fix _that_ problem.
> > Essentially, vpd_sections_init() should clean up after itself after it
> > fails to initialize a section.
> >
> > Note that I am not convinced that the "enabled" flag is needed in the first
> > place. It is only relevant if vpd_section_destroy() is called, which only
> > happens from the remove function. The remove function is only called if the
> > probe function succeeded. In that case it is always set for both sections.
> The problem will happen if coreboot memory changes between 2 probes so
> that header.ro_size is not 0 on the first pass and is 0 on the second
> pass. Not quite likely to ever happen in real life, but resetting a flag
> is pretty cheap to not do it.

If that can happen between probes, meaning it is not guaranteed to be
constant during the lifetime of the system, doesn't that mean it can
happen anytime ?


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