Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Zhenyu Wang]

On 2017.03.23 14:43:44 +0100, Frans Klaver wrote:
> On Thu, Mar 23, 2017 at 1:22 PM, Colin King  wrote:
> > From: Colin Ian King 
> >
> > info is being checked to see if it is a null pointer, however, vpgu is
> > dereferencing info before this check, leading to a potential null
> > pointer dereference.  If info is null, then the error message being
> > printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> > use a null vpgu as the macro has a sanity check to see if vpgu is null,
> > so this is OK.
> >
> > Detected with CoverityScan, CID#1420672 ("Dereference nefore null check")
> 
> s,nefore,before,
> 
> 
> >
> > Fixes: 695fbc08d80f ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
> > Signed-off-by: Colin Ian King 
> > ---
> >  drivers/gpu/drm/i915/gvt/kvmgt.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c 
> > b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > index 1ea3eb270de8..f8619a772c44 100644
> > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > @@ -1339,9 +1339,9 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
> >
> >  static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
> >  {
> > -   struct intel_vgpu *vgpu = info->vgpu;
> > -
> > if (!info) {
> > +   struct intel_vgpu *vgpu = NULL;
> > +
> > gvt_vgpu_err("kvmgt_guest_info invalid\n");
> > return false;
> > }
> 
> Does this mean the original gvt_err() macro is no longer there?
> 
> And apparently gvt_vgpu_err is a macro that depends on the specifics
> of its environment? Yikes.
> 

The null check is redundant there, we can just remove that block and extra
vgpu variable.

-- 
Open Source Technology Center, Intel ltd.

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Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Zhenyu Wang]

On 2017.03.23 14:43:44 +0100, Frans Klaver wrote:
> On Thu, Mar 23, 2017 at 1:22 PM, Colin King  wrote:
> > From: Colin Ian King 
> >
> > info is being checked to see if it is a null pointer, however, vpgu is
> > dereferencing info before this check, leading to a potential null
> > pointer dereference.  If info is null, then the error message being
> > printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> > use a null vpgu as the macro has a sanity check to see if vpgu is null,
> > so this is OK.
> >
> > Detected with CoverityScan, CID#1420672 ("Dereference nefore null check")
> 
> s,nefore,before,
> 
> 
> >
> > Fixes: 695fbc08d80f ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
> > Signed-off-by: Colin Ian King 
> > ---
> >  drivers/gpu/drm/i915/gvt/kvmgt.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c 
> > b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > index 1ea3eb270de8..f8619a772c44 100644
> > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> > @@ -1339,9 +1339,9 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
> >
> >  static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
> >  {
> > -   struct intel_vgpu *vgpu = info->vgpu;
> > -
> > if (!info) {
> > +   struct intel_vgpu *vgpu = NULL;
> > +
> > gvt_vgpu_err("kvmgt_guest_info invalid\n");
> > return false;
> > }
> 
> Does this mean the original gvt_err() macro is no longer there?
> 
> And apparently gvt_vgpu_err is a macro that depends on the specifics
> of its environment? Yikes.
> 

The null check is redundant there, we can just remove that block and extra
vgpu variable.

-- 
Open Source Technology Center, Intel ltd.

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Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Frans Klaver]

On Thu, Mar 23, 2017 at 1:22 PM, Colin King  wrote:
> From: Colin Ian King 
>
> info is being checked to see if it is a null pointer, however, vpgu is
> dereferencing info before this check, leading to a potential null
> pointer dereference.  If info is null, then the error message being
> printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> use a null vpgu as the macro has a sanity check to see if vpgu is null,
> so this is OK.
>
> Detected with CoverityScan, CID#1420672 ("Dereference nefore null check")

s,nefore,before,


>
> Fixes: 695fbc08d80f ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
> Signed-off-by: Colin Ian King 
> ---
>  drivers/gpu/drm/i915/gvt/kvmgt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c 
> b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 1ea3eb270de8..f8619a772c44 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1339,9 +1339,9 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
>
>  static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
>  {
> -   struct intel_vgpu *vgpu = info->vgpu;
> -
> if (!info) {
> +   struct intel_vgpu *vgpu = NULL;
> +
> gvt_vgpu_err("kvmgt_guest_info invalid\n");
> return false;
> }

Does this mean the original gvt_err() macro is no longer there?

And apparently gvt_vgpu_err is a macro that depends on the specifics
of its environment? Yikes.

Cheers,
Frans

Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Frans Klaver]

On Thu, Mar 23, 2017 at 1:22 PM, Colin King  wrote:
> From: Colin Ian King 
>
> info is being checked to see if it is a null pointer, however, vpgu is
> dereferencing info before this check, leading to a potential null
> pointer dereference.  If info is null, then the error message being
> printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> use a null vpgu as the macro has a sanity check to see if vpgu is null,
> so this is OK.
>
> Detected with CoverityScan, CID#1420672 ("Dereference nefore null check")

s,nefore,before,


>
> Fixes: 695fbc08d80f ("drm/i915/gvt: replace the gvt_err with gvt_vgpu_err")
> Signed-off-by: Colin Ian King 
> ---
>  drivers/gpu/drm/i915/gvt/kvmgt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c 
> b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 1ea3eb270de8..f8619a772c44 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1339,9 +1339,9 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
>
>  static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
>  {
> -   struct intel_vgpu *vgpu = info->vgpu;
> -
> if (!info) {
> +   struct intel_vgpu *vgpu = NULL;
> +
> gvt_vgpu_err("kvmgt_guest_info invalid\n");
> return false;
> }

Does this mean the original gvt_err() macro is no longer there?

And apparently gvt_vgpu_err is a macro that depends on the specifics
of its environment? Yikes.

Cheers,
Frans

Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Chris Wilson]

On Thu, Mar 23, 2017 at 12:22:30PM +, Colin King wrote:
> From: Colin Ian King 
> 
> info is being checked to see if it is a null pointer, however, vpgu is
> dereferencing info before this check, leading to a potential null
> pointer dereference.  If info is null, then the error message being
> printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> use a null vpgu as the macro has a sanity check to see if vpgu is null,
> so this is OK.

It is never NULL, it gets checked by its only caller.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH] drm/i915/kvmgt: avoid dereferencing a potentially null info pointer

[Chris Wilson]

On Thu, Mar 23, 2017 at 12:22:30PM +, Colin King wrote:
> From: Colin Ian King 
> 
> info is being checked to see if it is a null pointer, however, vpgu is
> dereferencing info before this check, leading to a potential null
> pointer dereference.  If info is null, then the error message being
> printed by macro gvt_vgpu_err and this requires vpgu to exist. We can
> use a null vpgu as the macro has a sanity check to see if vpgu is null,
> so this is OK.

It is never NULL, it gets checked by its only caller.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre