[PATCH 31/32] xenbus: Use mem_to_flex_dup() with struct read_buffer

[Kees Cook <keescook@xxxxxxxxxxxx>]

As part of the work to perform bounds checking on all memcpy() uses,
replace the open-coded a deserialization of bytes out of memory into a
trailing flexible array by using a flex_array.h helper to perform the
allocation, bounds checking, and copying.

Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 597af455a522..4267aaef33fb 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -81,8 +81,8 @@ struct xenbus_transaction_holder {
 struct read_buffer {
 	struct list_head list;
 	unsigned int cons;
-	unsigned int len;
-	char msg[];
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(unsigned int, len);
+	DECLARE_FLEX_ARRAY_ELEMENTS(char, msg);
 };
 
 struct xenbus_file_priv {
@@ -188,21 +188,17 @@ static ssize_t xenbus_file_read(struct file *filp,
  */
 static int queue_reply(struct list_head *queue, const void *data, size_t len)
 {
-	struct read_buffer *rb;
+	struct read_buffer *rb = NULL;
 
 	if (len == 0)
 		return 0;
 	if (len > XENSTORE_PAYLOAD_MAX)
 		return -EINVAL;
 
-	rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL);
-	if (rb == NULL)
+	if (mem_to_flex_dup(&rb, data, len, GFP_KERNEL))
 		return -ENOMEM;
 
 	rb->cons = 0;
-	rb->len = len;
-
-	memcpy(rb->msg, data, len);
 
 	list_add_tail(&rb->list, queue);
 	return 0;
-- 
2.32.0