[PATCH net-next v7] hv_netvsc: fix netvsc_send_completion to avoid multiple message length checks

[Sonia Sharma <sosha@linux.microsoft.com>]

From: Sonia Sharma <sonia.sharma@linux.microsoft.com>

The switch statement in netvsc_send_completion() is incorrectly validating
the length of incoming network packets by falling through to the next case.
Avoid the fallthrough. Instead break after a case match and then process
the complete() call.
The current code has not caused any known failures. But nonetheless, the
code should be corrected as a different ordering of the switch cases might
cause a length check to fail when it should not.

Signed-off-by: Sonia Sharma <sonia.sharma@linux.microsoft.com>

---
Changes in v3:
* added return statement in default case as pointed by Michael Kelley.
Changes in v4:
* added fixes tag
* modified commit message to explain the issue fixed by patch.
Changes in v5:
* Dropped fixes tag as suggested by Simon Horman.
* fixed indentation
Changes in v7:
* Dropped the prefix "net" from subject line.
---
 drivers/net/hyperv/netvsc.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index 82e9796c8f5e..0f7e4d377776 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -851,7 +851,7 @@ static void netvsc_send_completion(struct net_device *ndev,
 				   msglen);
 			return;
 		}
-		fallthrough;
+		break;
 
 	case NVSP_MSG1_TYPE_SEND_RECV_BUF_COMPLETE:
 		if (msglen < sizeof(struct nvsp_message_header) +
@@ -860,7 +860,7 @@ static void netvsc_send_completion(struct net_device *ndev,
 				   msglen);
 			return;
 		}
-		fallthrough;
+		break;
 
 	case NVSP_MSG1_TYPE_SEND_SEND_BUF_COMPLETE:
 		if (msglen < sizeof(struct nvsp_message_header) +
@@ -869,7 +869,7 @@ static void netvsc_send_completion(struct net_device *ndev,
 				   msglen);
 			return;
 		}
-		fallthrough;
+		break;
 
 	case NVSP_MSG5_TYPE_SUBCHANNEL:
 		if (msglen < sizeof(struct nvsp_message_header) +
@@ -878,10 +878,6 @@ static void netvsc_send_completion(struct net_device *ndev,
 				   msglen);
 			return;
 		}
-		/* Copy the response back */
-		memcpy(&net_device->channel_init_pkt, nvsp_packet,
-		       sizeof(struct nvsp_message));
-		complete(&net_device->channel_init_wait);
 		break;
 
 	case NVSP_MSG1_TYPE_SEND_RNDIS_PKT_COMPLETE:
@@ -904,13 +900,19 @@ static void netvsc_send_completion(struct net_device *ndev,
 
 		netvsc_send_tx_complete(ndev, net_device, incoming_channel,
 					desc, budget);
-		break;
+		return;
 
 	default:
 		netdev_err(ndev,
 			   "Unknown send completion type %d received!!\n",
 			   nvsp_packet->hdr.msg_type);
+		return;
 	}
+
+	/* Copy the response back */
+	memcpy(&net_device->channel_init_pkt, nvsp_packet,
+	       sizeof(struct nvsp_message));
+	complete(&net_device->channel_init_wait);
 }
 
 static u32 netvsc_get_next_send_section(struct netvsc_device *net_device)
-- 
2.25.1