2022-03-28 11:39:26

by Xiaomeng Tong

Subject: [PATCH] tilcdc: tilcdc_external: fix an incorrect NULL check on list iterator

The bug is here:
if (!encoder) {

The list iterator value 'encoder' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty or no element
is found.

To fix the bug, use a new variable 'iter' as the list iterator,
while use the original variable 'encoder' as a dedicated pointer
to point to the found element.

Cc: [email protected]
Fixes: ec9eab097a500 ("drm/tilcdc: Add drm bridge support for attaching drm bridge drivers")
Signed-off-by: Xiaomeng Tong <[email protected]>
---
drivers/gpu/drm/tilcdc/tilcdc_external.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_external.c b/drivers/gpu/drm/tilcdc/tilcdc_external.c
index 7594cf6e186e..3b86d002ef62 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_external.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_external.c
@@ -60,11 +60,13 @@ struct drm_connector *tilcdc_encoder_find_connector(struct drm_device *ddev,
int tilcdc_add_component_encoder(struct drm_device *ddev)
{
struct tilcdc_drm_private *priv = ddev->dev_private;
- struct drm_encoder *encoder;
+ struct drm_encoder *encoder = NULL, *iter;

- list_for_each_entry(encoder, &ddev->mode_config.encoder_list, head)
- if (encoder->possible_crtcs & (1 << priv->crtc->index))
+ list_for_each_entry(iter, &ddev->mode_config.encoder_list, head)
+ if (iter->possible_crtcs & (1 << priv->crtc->index)) {
+ encoder = iter;
break;
+ }

if (!encoder) {
dev_err(ddev->dev, "%s: No suitable encoder found\n", __func__);
--
2.17.1

2022-03-28 15:45:13

by Jyri Sarha

Subject: Re: [PATCH] tilcdc: tilcdc_external: fix an incorrect NULL check on list iterator

On 2022-03-27 9:15, Xiaomeng Tong wrote:
> The bug is here:
> if (!encoder) {
>
> The list iterator value 'encoder' will *always* be set and non-NULL
> by list_for_each_entry(), so it is incorrect to assume that the
> iterator value will be NULL if the list is empty or no element
> is found.
>
> To fix the bug, use a new variable 'iter' as the list iterator,
> while use the original variable 'encoder' as a dedicated pointer
> to point to the found element.
>
> Cc: [email protected]
> Fixes: ec9eab097a500 ("drm/tilcdc: Add drm bridge support for
> attaching drm bridge drivers")
> Signed-off-by: Xiaomeng Tong <[email protected]>

Thanks for the patch. Good catch.

Reviewed-by: Jyri Sarha <[email protected]>
Tested-by: Jyri Sarha <[email protected]>

I'll apply this to drm-misc-next in couple of days.

Best regards,
Jyri

> ---
> drivers/gpu/drm/tilcdc/tilcdc_external.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_external.c
> b/drivers/gpu/drm/tilcdc/tilcdc_external.c
> index 7594cf6e186e..3b86d002ef62 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_external.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_external.c
> @@ -60,11 +60,13 @@ struct drm_connector
> *tilcdc_encoder_find_connector(struct drm_device *ddev,
> int tilcdc_add_component_encoder(struct drm_device *ddev)
> {
> struct tilcdc_drm_private *priv = ddev->dev_private;
> - struct drm_encoder *encoder;
> + struct drm_encoder *encoder = NULL, *iter;
>
> - list_for_each_entry(encoder, &ddev->mode_config.encoder_list, head)
> - if (encoder->possible_crtcs & (1 << priv->crtc->index))
> + list_for_each_entry(iter, &ddev->mode_config.encoder_list, head)
> + if (iter->possible_crtcs & (1 << priv->crtc->index)) {
> + encoder = iter;
> break;
> + }
>
> if (!encoder) {
> dev_err(ddev->dev, "%s: No suitable encoder found\n", __func__);