[PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Zhou Qingyang]

In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
formats and used in drm_universal_plane_init().
drm_universal_plane_init() passes formats to
__drm_universal_plane_init(). __drm_universal_plane_init() further
passes formats to memcpy() as src parameter, which could lead to an
undefined behavior bug on failure of komeda_get_layer_fourcc_list().

Fix this bug by adding a check of formats.

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
 drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
index d63d83800a8a..dd3f17e970dd 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
@@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
 
 	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
 					       layer->layer_type, &n_formats);
+	if (!formats) {
+		err = -ENOMEM;
+		goto cleanup;
+	}
 
 	err = drm_universal_plane_init(&kms->base, plane,
 			get_possible_crtcs(kms, c->pipeline),
-- 
2.25.1

Re: [PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Steven Price]

On 30/11/2021 14:25, Zhou Qingyang wrote:
> In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
> formats and used in drm_universal_plane_init().
> drm_universal_plane_init() passes formats to
> __drm_universal_plane_init(). __drm_universal_plane_init() further
> passes formats to memcpy() as src parameter, which could lead to an
> undefined behavior bug on failure of komeda_get_layer_fourcc_list().
> 
> Fix this bug by adding a check of formats.
> 
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
> Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> index d63d83800a8a..dd3f17e970dd 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> @@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
>  
>  	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
>  					       layer->layer_type, &n_formats);
> +	if (!formats) {
> +		err = -ENOMEM;
> +		goto cleanup;
> +	}

If this executes it will cause undefined behaviour...

The cleanup code calls komeda_plane_destroy() which calls
drm_plane_cleanup() which does (amongst other things) a
list_del(&plane->head). But the plane hasn't been put on a list yet as
that's done in drm_universal_plane_init().

So in this case we simple want to do:

if (!formats) {
	kfree(kplane);
	return -ENOMEM;
}

Note that without this 'fix' a NULL return from
komeda_get_layer_fourcc_list() would leave n_formats==0, so while the
NULL pointer is passed into memcpy() it is also passed a length of 0.
Which I believe is safe.

However while looking at this function...

>  
>  	err = drm_universal_plane_init(&kms->base, plane,
>  			get_possible_crtcs(kms, c->pipeline),
> 

This call to drm_universal_plane_init() can fail early before
plane->head has been initialised. In which case the following:

> 	komeda_put_fourcc_list(formats);
> 
> 	if (err)
> 		goto cleanup;

commits the exact same sin and would cause a similar NULL dereference in
drm_plane_cleanup().

Steve

Re: [PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Liviu Dudau]

On Wed, Dec 01, 2021 at 03:44:03PM +0000, Steven Price wrote:
> On 30/11/2021 14:25, Zhou Qingyang wrote:
> > In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
> > formats and used in drm_universal_plane_init().
> > drm_universal_plane_init() passes formats to
> > __drm_universal_plane_init(). __drm_universal_plane_init() further
> > passes formats to memcpy() as src parameter, which could lead to an
> > undefined behavior bug on failure of komeda_get_layer_fourcc_list().
> > 
> > Fix this bug by adding a check of formats.
> > 
> > This bug was found by a static analyzer. The analysis employs
> > differential checking to identify inconsistent security operations
> > (e.g., checks or kfrees) between two code paths and confirms that the
> > inconsistent operations are not recovered in the current function or
> > the callers, so they constitute bugs.
> > 
> > Note that, as a bug found by static analysis, it can be a false
> > positive or hard to trigger. Multiple researchers have cross-reviewed
> > the bug.
> > 
> > Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
> > and our static analyzer no longer warns about this code.
> > 
> > Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
> > Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> > ---
> >  drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> > index d63d83800a8a..dd3f17e970dd 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> > @@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
> >  
> >  	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
> >  					       layer->layer_type, &n_formats);
> > +	if (!formats) {
> > +		err = -ENOMEM;
> > +		goto cleanup;
> > +	}
> 
> If this executes it will cause undefined behaviour...
> 
> The cleanup code calls komeda_plane_destroy() which calls
> drm_plane_cleanup() which does (amongst other things) a
> list_del(&plane->head). But the plane hasn't been put on a list yet as
> that's done in drm_universal_plane_init().
> 
> So in this case we simple want to do:
> 
> if (!formats) {
> 	kfree(kplane);
> 	return -ENOMEM;
> }

Zhou has already posted v2 that contains this fix.

> 
> Note that without this 'fix' a NULL return from
> komeda_get_layer_fourcc_list() would leave n_formats==0, so while the
> NULL pointer is passed into memcpy() it is also passed a length of 0.
> Which I believe is safe.
> 
> However while looking at this function...
> 
> >  
> >  	err = drm_universal_plane_init(&kms->base, plane,
> >  			get_possible_crtcs(kms, c->pipeline),
> > 
> 
> This call to drm_universal_plane_init() can fail early before
> plane->head has been initialised. In which case the following:
> 
> > 	komeda_put_fourcc_list(formats);
> > 
> > 	if (err)
> > 		goto cleanup;
> 
> commits the exact same sin and would cause a similar NULL dereference in
> drm_plane_cleanup().

I will come up with a patch for this case and post it to the list tomorrow.

Best regards,
Liviu



> 
> Steve

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

Re: [PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Steven Price]

On 01/12/2021 21:15, Liviu Dudau wrote:
> On Wed, Dec 01, 2021 at 03:44:03PM +0000, Steven Price wrote:
>> On 30/11/2021 14:25, Zhou Qingyang wrote:
>>> In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
>>> formats and used in drm_universal_plane_init().
>>> drm_universal_plane_init() passes formats to
>>> __drm_universal_plane_init(). __drm_universal_plane_init() further
>>> passes formats to memcpy() as src parameter, which could lead to an
>>> undefined behavior bug on failure of komeda_get_layer_fourcc_list().
>>>
>>> Fix this bug by adding a check of formats.
>>>
>>> This bug was found by a static analyzer. The analysis employs
>>> differential checking to identify inconsistent security operations
>>> (e.g., checks or kfrees) between two code paths and confirms that the
>>> inconsistent operations are not recovered in the current function or
>>> the callers, so they constitute bugs.
>>>
>>> Note that, as a bug found by static analysis, it can be a false
>>> positive or hard to trigger. Multiple researchers have cross-reviewed
>>> the bug.
>>>
>>> Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
>>> and our static analyzer no longer warns about this code.
>>>
>>> Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
>>> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
>>> ---
>>>  drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
>>> index d63d83800a8a..dd3f17e970dd 100644
>>> --- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
>>> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
>>> @@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
>>>  
>>>  	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
>>>  					       layer->layer_type, &n_formats);
>>> +	if (!formats) {
>>> +		err = -ENOMEM;
>>> +		goto cleanup;
>>> +	}
>>
>> If this executes it will cause undefined behaviour...
>>
>> The cleanup code calls komeda_plane_destroy() which calls
>> drm_plane_cleanup() which does (amongst other things) a
>> list_del(&plane->head). But the plane hasn't been put on a list yet as
>> that's done in drm_universal_plane_init().
>>
>> So in this case we simple want to do:
>>
>> if (!formats) {
>> 	kfree(kplane);
>> 	return -ENOMEM;
>> }
> 
> Zhou has already posted v2 that contains this fix.

Sorry, for some reason Zhou's patch appeared twice on the list and I
hadn't spotted your reply to the other version. My mistake.

>>
>> Note that without this 'fix' a NULL return from
>> komeda_get_layer_fourcc_list() would leave n_formats==0, so while the
>> NULL pointer is passed into memcpy() it is also passed a length of 0.
>> Which I believe is safe.
>>
>> However while looking at this function...
>>
>>>  
>>>  	err = drm_universal_plane_init(&kms->base, plane,
>>>  			get_possible_crtcs(kms, c->pipeline),
>>>
>>
>> This call to drm_universal_plane_init() can fail early before
>> plane->head has been initialised. In which case the following:
>>
>>> 	komeda_put_fourcc_list(formats);
>>>
>>> 	if (err)
>>> 		goto cleanup;
>>
>> commits the exact same sin and would cause a similar NULL dereference in
>> drm_plane_cleanup().
> 
> I will come up with a patch for this case and post it to the list tomorrow.

Great, thanks for taking a look - I'm afraid I couldn't see an obvious fix.

Regards,

Steven

Re: [PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Liviu Dudau]

Hi Zhou,

On Tue, Nov 30, 2021 at 10:23:01PM +0800, Zhou Qingyang wrote:
> In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
> formats and used in drm_universal_plane_init().
> drm_universal_plane_init() passes formats to
> __drm_universal_plane_init(). __drm_universal_plane_init() further
> passes formats to memcpy() as src parameter, which could lead to an
> undefined behavior bug on failure of komeda_get_layer_fourcc_list().
> 
> Fix this bug by adding a check of formats.
> 
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.

If multiple researchers have cross-reviewed the bug how many have reviewed the fix?
I'm asking because there is a problem with the fix ....


> 
> Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> index d63d83800a8a..dd3f17e970dd 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> @@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
>  
>  	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
>  					       layer->layer_type, &n_formats);
> +	if (!formats) {
> +		err = -ENOMEM;
> +		goto cleanup;

If you go to cleanup here it is too early, as the plane variable has not been
initialised by the drm_universal_plane_init(), so komeda_plane_destroy() will crash.
The correct fix here is to free the kplane allocation and then return -ENOMEM.

> +	}
>  
>  	err = drm_universal_plane_init(&kms->base, plane,
>  			get_possible_crtcs(kms, c->pipeline),
> -- 
> 2.25.1
> 

Best regards,
Liviu

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

[PATCH] drm/komeda: Fix an undefined behavior bug in komeda_plane_add()

[Zhou Qingyang]

In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to
formats and used in drm_universal_plane_init().
drm_universal_plane_init() passes formats to
__drm_universal_plane_init(). __drm_universal_plane_init() further
passes formats to memcpy() as src parameter, which could lead to an
undefined behavior bug on failure of komeda_get_layer_fourcc_list().

Fix this bug by adding a check of formats.

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_DRM_KOMEDA=m show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
 drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
index d63d83800a8a..dd3f17e970dd 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c
@@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
 
 	formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl,
 					       layer->layer_type, &n_formats);
+	if (!formats) {
+		err = -ENOMEM;
+		goto cleanup;
+	}
 
 	err = drm_universal_plane_init(&kms->base, plane,
 			get_possible_crtcs(kms, c->pipeline),
-- 
2.25.1