[PATCH] media: v4l: async: Fix NULL pointer dereference in adding ancillary links

[cy_huang]

From: ChiYuan Huang <cy_huang@xxxxxxxxxxx>

In v4l2_async_create_ancillary_links(), ancillary links are created for
lens and flash sub-devices. These are sub-device to sub-device links and if
the async notifier is related to a V4L2 device, the source sub-device of
the ancillary link is NULL, leading to a NULL pointer dereference. Check
the notifier's sd field is non-NULL in v4l2_async_create_ancillary_links().

Fixes: aa4faf6eb271 ("media: v4l2-async: Create links during v4l2_async_match_notify()")
Signed-off-by: ChiYuan Huang <cy_huang@xxxxxxxxxxx>
---
Hi:
  Following the comment to revise the patch title and commit message.

The previous patch discussion is at the below link.
https://lore.kernel.org/lkml/e2f9f2b7b7de956d70b8567a2ab285409fff988b.1715136478.git.cy_huang@xxxxxxxxxxx/
---
 drivers/media/v4l2-core/v4l2-async.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 3ec323bd528b..9d3161c51954 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -324,6 +324,9 @@ static int v4l2_async_create_ancillary_links(struct v4l2_async_notifier *n,
 	    sd->entity.function != MEDIA_ENT_F_FLASH)
 		return 0;
 
+	if (!n->sd)
+		return 0;
+
 	link = media_create_ancillary_link(&n->sd->entity, &sd->entity);
 
 #endif
-- 
2.34.1