[Freedreno] [PATCH] drm/msm: fix an error code in the ioctl

[Jordan Crouse]

On Thu, Feb 14, 2019 at 06:16:01PM -0500, Rob Clark wrote:
> On Thu, Feb 14, 2019 at 2:19 AM Dan Carpenter <dan.carpenter at oracle.com> wrote:
> >
> > The copy_to/from_user() functions return the number of bytes remaining
> > to be copied but we should return -EFAULT to the user.
> >
> > Fixes: f05c83e77460 ("drm/msm: add uapi to get/set debug name")
> > Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> > ---
> > If I were reviewing this patch, I would be suspicous that we don't
> > return immediately after the first copy_from_user() fails but I'm fairly
> > sure that is the correct behavior.
> 
> oh, hmm, you are defn right that the current code is incorrect..

This one was Boneheaded-by: me.

> Although I guess I wonder if maybe in the -EFAULT case we should set a
> null char at the end of the # of bytes copied in.  I guess the result
> with your patch as-is is that you'd get part of the new debug name
> string, and part of the old.  Which is maybe not incorrect or worse
> than truncated new debug name.  (It is really mostly just for debugfs
> after all.)

> I guess we could copy_from_user() into a temp buffer to leave the old
> debug name undisturbed in the -EFAULT case, but I'd accept he argument
> that that would be overkill.

Right. I think on failure we should just truncate the string back to strlen(0)
and pretend that nothing happened.  I can toss up a patch for that.

Jordan

> >
> >  drivers/gpu/drm/msm/msm_drv.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > index b871e2e98129..1d4426cb260d 100644
> > --- a/drivers/gpu/drm/msm/msm_drv.c
> > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > @@ -851,8 +851,9 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
> >                         ret = -EINVAL;
> >                         break;
> >                 }
> > -               ret = copy_from_user(msm_obj->name,
> > -                       u64_to_user_ptr(args->value), args->len);
> > +               if (copy_from_user(msm_obj->name, u64_to_user_ptr(args->value),
> > +                                  args->len))
> > +                       ret = -EFAULT;
> >                 msm_obj->name[args->len] = '\0';
> >                 for (i = 0; i < args->len; i++) {
> >                         if (!isprint(msm_obj->name[i])) {
> > @@ -868,8 +869,9 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
> >                 }
> >                 args->len = strlen(msm_obj->name);
> >                 if (args->value) {
> > -                       ret = copy_to_user(u64_to_user_ptr(args->value),
> > -                                       msm_obj->name, args->len);
> > +                       if (copy_to_user(u64_to_user_ptr(args->value),
> > +                                        msm_obj->name, args->len))
> > +                               ret = -EFAULT;
> >                 }
> >                 break;
> >         }
> > --
> > 2.17.1
> >
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