Re: [PATCH] drm/msm/adreno/a5xx_debugfs: fix potential NULL pointer dereference

[Gustavo A. R. Silva]

Quoting Rob Clark <robdclark@xxxxxxxxx>:

> On Fri, Feb 2, 2018 at 11:30 AM, Jordan Crouse  
> <jcrouse@xxxxxxxxxxxxxx> wrote:
> > On Fri, Feb 02, 2018 at 06:32:23AM -0600, Gustavo A. R. Silva wrote:
> > > _minor_ is being dereferenced before it is null checked, hence there
> > > is a potential null pointer dereference. Fix this by moving the pointer
> > > dereference after _minor_ has been null checked.
> > >
> > > Fixes: 024ad8df763f ("drm/msm: add a5xx specific debugfs")
> > > Signed-off-by: Gustavo A. R. Silva <garsilva@xxxxxxxxxxxxxx>
> > > ---
> > >
> > > I wonder if a better solution for this would be to WARN_ON in case _minor_
> > > happens to be NULL and return -EINVAL, instead of just returning zero.
> > >
> > > Something like:
> > >
> > > struct drm_device *dev;
> > >
> > > if (WARN_ON(!minor)
> > >       return -EINVAL;
> > >
> > > dev = minor->dev;
> > >
> > > What do you think?
> >
> > In my opinion everything in debugfs is optional. I'm not sure if it is even
> > possible for dev->primary, dev->render or dev->control to be NULL  
> > from the DRM
> > core but if so I think the failure should be silent.
>
> Don't have code in front of me atm, but I think this is one of those
> things you can hit both before and after we have the minor, depending
> on whether filesystem and fw are present when the driver loads or
> not.. so I don't think it should be a WARN_ON().

I get it. Then in this case this patch should work just fine.

Thank you both Jordan and Rob for the feedback.
--
Gustavo

> BR,
> -R
>
>
> > Jordan
> > >  drivers/gpu/drm/msm/adreno/a5xx_debugfs.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/adreno/a5xx_debugfs.c  
> > > b/drivers/gpu/drm/msm/adreno/a5xx_debugfs.c
> > > index 6b27941..059ec7d 100644
> > > --- a/drivers/gpu/drm/msm/adreno/a5xx_debugfs.c
> > > +++ b/drivers/gpu/drm/msm/adreno/a5xx_debugfs.c
> > > @@ -159,13 +159,15 @@ DEFINE_SIMPLE_ATTRIBUTE(reset_fops, NULL,  
> > > reset_set, "%llx\n");
> > >
> > >  int a5xx_debugfs_init(struct msm_gpu *gpu, struct drm_minor *minor)
> > >  {
> > > -     struct drm_device *dev = minor->dev;
> > > +     struct drm_device *dev;
> > >       struct dentry *ent;
> > >       int ret;
> > >
> > >       if (!minor)
> > >               return 0;
> > >
> > > +     dev = minor->dev;
> > > +
> > >       ret = drm_debugfs_create_files(a5xx_debugfs_list,
> > >                       ARRAY_SIZE(a5xx_debugfs_list),
> > >                       minor->debugfs_root, minor);
> > > --
> > > 2.7.4
> > >
> > > --
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