Re: [PATCH] libnvdimm/namespace: Fix a signedness bug in __holder_class_store()

[Ira Weiny <ira.weiny@intel.com>]

On Wed, Sep 25, 2019 at 10:49:08AM -0700, 'Vishal Verma' wrote:
> On Wed, 2019-09-25 at 11:25 -0600, Weiny, Ira wrote:
> > > On Wed, 2019-09-25 at 14:00 +0300, Dan Carpenter wrote:
> > > > The "ndns->claim_class" variable is an enum but in this case GCC will
> > > > treat it as an unsigned int so the error handling is never triggered.
> > > > 
> > > > Fixes: 14e494542636 ("libnvdimm, btt: BTT updates for UEFI 2.7
> > > > format")
> > > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > > ---
> > > >  drivers/nvdimm/namespace_devs.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/nvdimm/namespace_devs.c
> > > > b/drivers/nvdimm/namespace_devs.c index cca0a3ba1d2c..669985527716
> > > > 100644
> > > > --- a/drivers/nvdimm/namespace_devs.c
> > > > +++ b/drivers/nvdimm/namespace_devs.c
> > > > @@ -1529,7 +1529,7 @@ static ssize_t __holder_class_store(struct device
> > > *dev, const char *buf)
> > > >  		return -EINVAL;
> > > > 
> > > >  	/* btt_claim_class() could've returned an error */
> > > > -	if (ndns->claim_class < 0)
> > > > +	if ((int)ndns->claim_class < 0)
> > > >  		return ndns->claim_class;
> > > > 
> > > >  	return 0;
> > > 
> > > Looks straightforward, and a good catch.
> > > Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
> > 
> > I'm not sure this is really a good fix.  This leaves ndns->claim_class set to an invalid value.  Is that ok?
> > 
> 
> Hm, it is just in a store operation for the holder_class sysfs
> attribute. if claim_class was negative, that store will just fail.
> 
> From the userspace side, this means the 'mode' enforcement API will
> fail. Typically, 'ndctl' doesn't require the enforcement to succeed,
> since we can disambiguate namespaces even without it, so it doesn't
> block namespace creation etc.
> 
> On the kernel side, claim_class gets used by btt_devs.c during probe,
> and looks like this case, as it currently stands, would fail the BTT
> probe (nd_btt_probe()). I think this is what we want?
> 
> I guess it can be made a bit clearer by storing NVDIMM_CCLASS_UNKNOWN
> explicitly in holder_class_store(), but that can be a separate
> improvement from what this patch is addressing.

Fair enough I've sent a follow on patch.

Thanks,
Ira

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