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

[Jyri Sarha]

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: sta...@vger.kernel.org
Fixes: ec9eab097a500 ("drm/tilcdc: Add drm bridge support for
attaching drm bridge drivers")
Signed-off-by: Xiaomeng Tong <xiam0nd.t...@gmail.com>

Thanks for the patch. Good catch.

Reviewed-by: Jyri Sarha <jyri.sa...@iki.fi>
Tested-by: Jyri Sarha <jyri.sa...@iki.fi>

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__);