[PATCH v3] media: v4l2-subdev: Fix error check in v4l2_subdev_get_frame_desc_passthrough()

[Chen Ni <nichen@iscas.ac.cn>]

Use IS_ERR() and PTR_ERR() to properly handle the error return from
media_pad_remote_pad_unique(), which returns ERR_PTR() on failure but
never NULL. The previous code only checked for NULL, leading to invalid
pointer dereference.

Detected by Smatch:
drivers/media/v4l2-core/v4l2-subdev.c:2588 v4l2_subdev_get_frame_desc_passthrough() warn:
'remote_source_pad' is an error pointer or valid

drivers/media/v4l2-core/v4l2-subdev.c:2595 v4l2_subdev_get_frame_desc_passthrough() error:
'remote_source_pad' dereferencing possible ERR_PTR()

Fixes: a564839e630c ("media: subdev: Add v4l2_subdev_get_frame_desc_passthrough helper")
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
---
Changes in v3:
- Remove the Reported-by tag due to missing Closes: URL

Changes in v2:
- Added Smatch warning messages to commit message
- Added Reported-by tag for Ethan Tidmore
- Kept both Reviewed-by tags
---
 drivers/media/v4l2-core/v4l2-subdev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 9efd14d4026f..7cb17e0a5617 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -2585,10 +2585,10 @@ int v4l2_subdev_get_frame_desc_passthrough(struct v4l2_subdev *sd,
 
 			if (!have_source_fd) {
 				remote_source_pad = media_pad_remote_pad_unique(local_sink_pad);
-				if (!remote_source_pad) {
+				if (IS_ERR(remote_source_pad)) {
 					dev_dbg(dev, "Failed to find remote pad for sink pad %u\n",
 						local_sink_pad->index);
-					ret = -EINVAL;
+					ret = PTR_ERR(remote_source_pad);
 					goto out_unlock;
 				}
 
-- 
2.25.1