Re: [PATCH] cxl/hdm: Avoid NULL deref when component registers are missing

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 30 Mar 2023 11:19:42 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> Jonathan Cameron wrote:
> > On Wed, 29 Mar 2023 14:35:43 -0700
> > Dan Williams <dan.j.williams@intel.com> wrote:
> >   
> > > The cxl_port driver attempts to support endpoint devices that do not
> > > advertise a component register block, but by inspection
> > > devm_cxl_setup_hdm() passes a NULL @crb to helper functions that should
> > > be skipped.
> > > 
> > > Return early and skip setting target_count since that is only relevant
> > > for switch decoders, not endpoint decoders.  
> > 
> > This is a good observation. It would be nice to not read it for the
> > HDM decoder path either. Obviously we don't use it so that doesn't do
> > any harm, but to someone reading the code it looks like we care about the
> > value.  I'm not immediately sure how we'd establish at this layer that
> > the HDM decoder is a switch or HB one though..  
> 
> @info is NULL when this routine is called for non-endpoint decoders.

Ah, so we could pass a flag into parse_hdm_decoder_caps() and not read
the value if it has no meaning for the particular decoder.

> 
> > > Fixes: 757f6448b100 ("cxl/hdm: Fix double allocation of @cxlhdm")
> > > Tested-by: Dave Jiang <dave.jiang@intel.com>
> > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>  
> > Patch looks fine to me.
> > 
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>