linux-kernel - Re: [PATCH V4] drm/xe/guc: Fix dereference before NULL check

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Message-ID: <CAEO-vhGzRxths0OG_MJEPqocyQ5C0hDXvJRWfYYv74qnCbCVCg@mail.gmail.com>
Date: Wed, 23 Oct 2024 14:59:34 -0600
From: "Everest K.C." <everestkc@...restkc.com.np>
To: Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc: lucas.demarchi@...el.com, thomas.hellstrom@...ux.intel.com, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, 
	airlied@...il.com, simona@...ll.ch, skhan@...uxfoundation.org, 
	dan.carpenter@...aro.org, michal.wajdeczko@...el.com, 
	intel-xe@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] drm/xe/guc: Fix dereference before NULL check

On Wed, Oct 23, 2024 at 2:11 PM Rodrigo Vivi <rodrigo.vivi@...el.com> wrote:
>
> On Thu, Oct 10, 2024 at 10:57:59AM -0600, Everest K.C. wrote:
> > The pointer list->list is dereferenced before the NULL check.
> > Fix this by moving the NULL check outside the for loop, so that
> > the check is performed before the dereferencing.
> > The list->list pointer cannot be NULL so this has no effect on runtime.
> > It's just a correctness issue.
> >
> > This issue was reported by Coverity Scan.
> > https://scan7.scan.coverity.com/#/project-view/51525/11354?selectedIssue=1600335
> >
> > Fixes: 0f1fdf559225 ("drm/xe/guc: Save manual engine capture into capture list")
> > Signed-off-by: Everest K.C. <everestkc@...restkc.com.np>
> > Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
> > ---
> > V3 -> V4: - Corrected the Fixes tag
> >           - Added Reviewed-by tag
>
> For some reason it looks like nor CI nor lore has this v4 version.
Yeah, I just checked that and it's something strange.
> could you please resubmit it?
Yes, let me send it right away.
> > V2 -> V3: - Changed Null to NULL in the changelog
> >           - Corrected typo in the changelong
> >           - Added more description to the changelong
> >         - Fixed the link for Coverity Report
> >         - Removed the space after the Fixes tag
> > V1 -> V2: - Combined the `!list->list` check in preexisting if statement
> >         - Added Fixes tag
> >         - Added the link to the Coverity Scan report
> >
> >  drivers/gpu/drm/xe/xe_guc_capture.c | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/xe/xe_guc_capture.c b/drivers/gpu/drm/xe/xe_guc_capture.c
> > index 41262bda20ed..947c3a6d0e5a 100644
> > --- a/drivers/gpu/drm/xe/xe_guc_capture.c
> > +++ b/drivers/gpu/drm/xe/xe_guc_capture.c
> > @@ -1531,7 +1531,7 @@ read_reg_to_node(struct xe_hw_engine *hwe, const struct __guc_mmio_reg_descr_gro
> >  {
> >       int i;
> >
> > -     if (!list || list->num_regs == 0)
> > +     if (!list || !list->list || list->num_regs == 0)
> >               return;
> >
> >       if (!regs)
> > @@ -1541,9 +1541,6 @@ read_reg_to_node(struct xe_hw_engine *hwe, const struct __guc_mmio_reg_descr_gro
> >               struct __guc_mmio_reg_descr desc = list->list[i];
> >               u32 value;
> >
> > -             if (!list->list)
> > -                     return;
> > -
> >               if (list->type == GUC_STATE_CAPTURE_TYPE_ENGINE_INSTANCE) {
> >                       value = xe_hw_engine_mmio_read32(hwe, desc.reg);
> >               } else {
> > --
> > 2.43.0
> >

With Regards,
Everest K C