[PATCH] Prevent NULL MDL's from being queued for transmission.

[Martin Harvey <Martin.Harvey@xxxxxxxxxx>]

Under conditions of high load and low resources, it was
possible for NDIS (in combination with overlying drivers) to send
NET_BUFFER_LIST structures containing NULL MDL's for transmission.
This resulted in an immediate bugcheck.

This patch prevents NULL MDL's from being sent to XenVif.

Signed-off-by: Martin Harvey <martin.harvey@xxxxxxxxxx>
---
 src/xennet/transmitter.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/src/xennet/transmitter.c b/src/xennet/transmitter.c
index 0e184fd..334bbb9 100644
--- a/src/xennet/transmitter.c
+++ b/src/xennet/transmitter.c
@@ -323,17 +323,21 @@ __TransmitterSendNetBufferList(
 
         __TransmitterGetNetBufferList(Transmitter, NetBufferList);
 
-        status = XENVIF_VIF(TransmitterQueuePacket,
-                            AdapterGetVifInterface(Transmitter->Adapter),
-                            NET_BUFFER_CURRENT_MDL(NetBuffer),
-                            NET_BUFFER_CURRENT_MDL_OFFSET(NetBuffer),
-                            NET_BUFFER_DATA_LENGTH(NetBuffer),
-                            OffloadOptions,
-                            MaximumSegmentSize,
-                            TagControlInformation,
-                            &Hash,
-                            (NetBufferListNext != NULL) ? TRUE : FALSE,
-                            Cookie);
+        if (NET_BUFFER_CURRENT_MDL(NetBuffer) != NULL) {
+            status = XENVIF_VIF(TransmitterQueuePacket,
+                                AdapterGetVifInterface(Transmitter->Adapter),
+                                NET_BUFFER_CURRENT_MDL(NetBuffer),
+                                NET_BUFFER_CURRENT_MDL_OFFSET(NetBuffer),
+                                NET_BUFFER_DATA_LENGTH(NetBuffer),
+                                OffloadOptions,
+                                MaximumSegmentSize,
+                                TagControlInformation,
+                                &Hash,
+                                (NetBufferListNext != NULL) ? TRUE : FALSE,
+                                Cookie);
+        }
+        else
+            status = STATUS_INVALID_PARAMETER;
         if (!NT_SUCCESS(status)) {
             __TransmitterReturnPacket(Transmitter, Cookie,
                                       NDIS_STATUS_NOT_ACCEPTED);
-- 
2.25.0.windows.1