[PATCH 2/4] staging: vc04_services: vchiq-mmal: add buffer size check in inline_receive()

[Sebastian Josue Alba Vives <sebasjosue84@gmail.com>]

From: Sebastián Alba Vives <sebasjosue84@gmail.com>

inline_receive() copies payload data from a VCHIQ message into a
destination buffer using payload_in_message as the copy length, but
never validates that this length fits within the destination buffer
(msg_context->u.bulk.buffer->buffer_size).

While the caller validates payload_in_message <= MMAL_VC_SHORT_DATA
(128) to prevent overreading the source, the destination buffer may be
smaller than 128 bytes. This is inconsistent with bulk_receive() which
does check buffer_size before copying. A VideoCore GPU sending a short
inline payload to a smaller destination buffer would cause a heap buffer
overflow in kernel memory.

Add a bounds check against buffer_size and truncate the copy length if
it exceeds the destination capacity, matching the defensive pattern used
in bulk_receive().

Fixes: b18ee53ad297 ("staging: bcm2835: Break MMAL support out from camera")
Signed-off-by: Sebastián Alba Vives <sebasjosue84@gmail.com>
---
 .../vc04_services/vchiq-mmal/mmal-vchiq.c     | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/vc04_services/vchiq-mmal/mmal-vchiq.c b/drivers/staging/vc04_services/vchiq-mmal/mmal-vchiq.c
index 4772126d7..e18471930 100644
--- a/drivers/staging/vc04_services/vchiq-mmal/mmal-vchiq.c
+++ b/drivers/staging/vc04_services/vchiq-mmal/mmal-vchiq.c
@@ -368,12 +368,26 @@ static int inline_receive(struct vchiq_mmal_instance *instance,
 			  struct mmal_msg *msg,
 			  struct mmal_msg_context *msg_context)
 {
+	u32 payload_len = msg->u.buffer_from_host.payload_in_message;
+
+	/*
+	 * Ensure the payload fits within the destination buffer.
+	 * The caller already validates payload_len <= MMAL_VC_SHORT_DATA
+	 * against the source, but the destination buffer may be smaller.
+	 * bulk_receive() performs this check; inline_receive() must too.
+	 */
+	if (payload_len > msg_context->u.bulk.buffer->buffer_size) {
+		payload_len = msg_context->u.bulk.buffer->buffer_size;
+		pr_warn("inline_receive: payload truncated (%u > %lu)\n",
+			msg->u.buffer_from_host.payload_in_message,
+			msg_context->u.bulk.buffer->buffer_size);
+	}
+
 	memcpy(msg_context->u.bulk.buffer->buffer,
 	       msg->u.buffer_from_host.short_data,
-	       msg->u.buffer_from_host.payload_in_message);
+	       payload_len);
 
-	msg_context->u.bulk.buffer_used =
-	    msg->u.buffer_from_host.payload_in_message;
+	msg_context->u.bulk.buffer_used = payload_len;
 
 	return 0;
 }
-- 
2.43.0