[PATCH] media: bcm2835-unicam: fix dummy buffer double free when register fails

[Dawei Feng]

unicam_register_node() allocates node->dummy_buf_cpu_addr before
registering the video device. If video_register_device() fails, the
error path frees the dummy buffer but leaves the pointer unchanged.
unicam_async_complete() then unwinds the partial setup through
unicam_unregister_nodes(), which sees the stale non-NULL pointer and
frees the same buffer again.

Set dummy_buf_cpu_addr to NULL after dma_free_coherent() in both the
local error path and unicam_unregister_nodes() so later cleanup skips
already released buffers.

The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1-rc3.

Runtime validation was not attempted because reproducing this failure
path requires fault injection in a hardware-specific driver.

Fixes: 392cd78d495f ("media: bcm2835-unicam: Add support for CCP2/CSI2 camera interface")
Cc: stable at vger.kernel.org
Signed-off-by: Zilin Guan <zilin at seu.edu.cn>
Signed-off-by: Dawei Feng <dawei.feng at seu.edu.cn>
---
 drivers/media/platform/broadcom/bcm2835-unicam.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
index 8d28ba0b59a3..94c80601c50d 100644
--- a/drivers/media/platform/broadcom/bcm2835-unicam.c
+++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
@@ -2360,6 +2360,7 @@ static int unicam_register_node(struct unicam_device *unicam,
 	dma_free_coherent(unicam->dev, node->dummy_buf.size,
 			  node->dummy_buf_cpu_addr,
 			  node->dummy_buf.dma_addr);
+	node->dummy_buf_cpu_addr = NULL;
 err_entity_cleanup:
 	media_entity_cleanup(&vdev->entity);
 err_unicam_put:
@@ -2379,10 +2380,12 @@ static void unicam_unregister_nodes(struct unicam_device *unicam)
 			node->registered = false;
 		}
 
-		if (node->dummy_buf_cpu_addr)
+		if (node->dummy_buf_cpu_addr) {
 			dma_free_coherent(unicam->dev, node->dummy_buf.size,
 					  node->dummy_buf_cpu_addr,
 					  node->dummy_buf.dma_addr);
+			node->dummy_buf_cpu_addr = NULL;
+		}
 	}
 }
 
-- 
2.34.1