[PATCH] kdbus: properly reset metadata iovecs on multicasts

[David Herrmann <dh.herrmann@gmail.com>]

If a message is sent to multiple destinations, each destination might
request a different set of metadata. Hence, we cannot rely on each one
requesting at least a single bit.

Fix the message exporter to properly reset the metadata iovec on each
emit-iteration. Otherwise, we might end up scanning random heap memory if
a following destination does not request metadata.

Reported-by: Jan Alexander Steffens <jan.steffens@gmail.com>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
Hi Greg

One fall-out from the rewrite of the message importer. Reported by Jan. This
fixes some issues with metadata on messages targeted at more than one
destination. Reproducible by running a debug-monitor (which thus gets any
messages, additionally to the normal receiver).

Thanks
David

 ipc/kdbus/message.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/ipc/kdbus/message.c b/ipc/kdbus/message.c
index 64763ea..3520f45 100644
--- a/ipc/kdbus/message.c
+++ b/ipc/kdbus/message.c
@@ -946,6 +946,16 @@ struct kdbus_pool_slice *kdbus_staging_emit(struct kdbus_staging *staging,
 		++v;
 
 		msg_size = KDBUS_ALIGN8(msg_size) + meta_size;
+	} else {
+		/* metadata items */
+		v->iov_len = 0;
+		v->iov_base = (void __user *)zeros;
+		++v;
+
+		/* padding after metadata */
+		v->iov_len = 0;
+		v->iov_base = (void __user *)zeros;
+		++v;
 	}
 
 	/* ... payload iovecs are already filled in ... */
-- 
2.4.5