[PATCH 25/32] Drivers: hv: utils: Use mem_to_flex_dup() with struct cn_msg

[Kees Cook]

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: "K. Y. Srinivasan" <kys at microsoft.com>
Cc: Haiyang Zhang <haiyangz at microsoft.com>
Cc: Stephen Hemminger <sthemmin at microsoft.com>
Cc: Wei Liu <wei.liu at kernel.org>
Cc: Dexuan Cui <decui at microsoft.com>
Cc: linux-hyperv at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 drivers/hv/hv_utils_transport.c | 7 ++-----
 include/uapi/linux/connector.h  | 4 ++--
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/hv/hv_utils_transport.c b/drivers/hv/hv_utils_transport.c
index 832885198643..43b4f8893cc0 100644
--- a/drivers/hv/hv_utils_transport.c
+++ b/drivers/hv/hv_utils_transport.c
@@ -217,20 +217,17 @@ static void hvt_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 int hvutil_transport_send(struct hvutil_transport *hvt, void *msg, int len,
 			  void (*on_read_cb)(void))
 {
-	struct cn_msg *cn_msg;
+	struct cn_msg *cn_msg = NULL;
 	int ret = 0;
 
 	if (hvt->mode == HVUTIL_TRANSPORT_INIT ||
 	    hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
 		return -EINVAL;
 	} else if (hvt->mode == HVUTIL_TRANSPORT_NETLINK) {
-		cn_msg = kzalloc(sizeof(*cn_msg) + len, GFP_ATOMIC);
-		if (!cn_msg)
+		if (mem_to_flex_dup(&cn_msg, msg, len, GFP_ATOMIC))
 			return -ENOMEM;
 		cn_msg->id.idx = hvt->cn_id.idx;
 		cn_msg->id.val = hvt->cn_id.val;
-		cn_msg->len = len;
-		memcpy(cn_msg->data, msg, len);
 		ret = cn_netlink_send(cn_msg, 0, 0, GFP_ATOMIC);
 		kfree(cn_msg);
 		/*
diff --git a/include/uapi/linux/connector.h b/include/uapi/linux/connector.h
index 3738936149a2..b85bbe753dae 100644
--- a/include/uapi/linux/connector.h
+++ b/include/uapi/linux/connector.h
@@ -73,9 +73,9 @@ struct cn_msg {
 	__u32 seq;
 	__u32 ack;
 
-	__u16 len;		/* Length of the following data */
+	__DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(__u16, len);
 	__u16 flags;
-	__u8 data[0];
+	__DECLARE_FLEX_ARRAY_ELEMENTS(__u8, data);
 };
 
 #endif /* _UAPI__CONNECTOR_H */
-- 
2.32.0