[PATCH] drm/i915: do not return invalid pointers as a *dentry

[Greg Kroah-Hartman]

On Thu, Jan 31, 2019 at 09:59:26AM -0800, Rodrigo Vivi wrote:
> On Thu, Jan 31, 2019 at 02:15:07PM +0100, Greg Kroah-Hartman wrote:
> > When calling debugfs functions, they can now return error values if
> > something went wrong.  If that happens, return a NULL as a *dentry to
> > the relay core instead of passing it an illegal pointer.
> > 
> > The relay core should be able to handle an illegal pointer, but add this
> > check to be safe.
> > 
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Cc: David Airlie <airlied at linux.ie>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Cc: intel-gfx at lists.freedesktop.org
> > Cc: dri-devel at lists.freedesktop.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> > ---
> >  drivers/gpu/drm/i915/intel_guc_log.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_guc_log.c b/drivers/gpu/drm/i915/intel_guc_log.c
> > index d3ebdbc0182e..8bf03497dcd8 100644
> > --- a/drivers/gpu/drm/i915/intel_guc_log.c
> > +++ b/drivers/gpu/drm/i915/intel_guc_log.c
> > @@ -140,6 +140,9 @@ static struct dentry *create_buf_file_callback(const char *filename,
> >  
> >  	buf_file = debugfs_create_file(filename, mode,
> >  				       parent, buf, &relay_file_operations);
> > +	if (IS_ERR(buf_file))
> > +		return NULL;
> 
> I still see a return NULL inside debugfs_create_file on master,
> but probably you are ahead with some change that I didn't see yet right?

Yes, this patch is in linux-next now and should go to Linus for
5.0-final:
	https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git/commit/?h=driver-core-linus&id=ff9fb72bc07705c00795ca48631f7fffe24d2c6b

> I'm just wondering if it wouldn't be better for now to go with
> 
> if (IS_ERR_OR_NULL(buf_file))

Not really, because the next line is:

> >  	return buf_file;

So it's the same thing :)

> apparently we also need it on i915_debugfs.c i915_debugfs_register()

I have a bunch of patches I'm working on to go through and fix up all of
this (you shouldn't be checking the return value at all, unless you
really want to use it as a "real" dentry and not just something that
debugfs uses internally.

But for now, you should be fine, that call will only fail if you are out
of memory, or did something really wrong.

thanks,

greg k-h