[pschweitzer] 69480: [MSFS] Prevent a race condition on reading message from list. Spotted by Thomas

Author: pschweitzer
Date: Sat Oct 10 12:08:45 2015
New Revision: 69480

URL: http://svn.reactos.org/svn/reactos?rev=69480&view=rev
Log:
[MSFS]
Prevent a race condition on reading message from list.
Spotted by Thomas

Modified:
    trunk/reactos/drivers/filesystems/msfs/rw.c

Modified: trunk/reactos/drivers/filesystems/msfs/rw.c
URL:
http://svn.reactos.org/svn/reactos/trunk/reactos/drivers/filesystems/msfs/r…
==============================================================================
--- trunk/reactos/drivers/filesystems/msfs/rw.c	[iso-8859-1] (original)
+++ trunk/reactos/drivers/filesystems/msfs/rw.c	[iso-8859-1] Sat Oct 10 12:08:45 2015
@@ -33,6 +33,7 @@
     PKTIMER Timer;
     PMSFS_DPC_CTX Context;
     PKDPC Dpc;
+    PLIST_ENTRY Entry;
 
     DPRINT("MsfsRead(DeviceObject %p Irp %p)\n", DeviceObject, Irp);
 
@@ -63,17 +64,14 @@
 
     if (Fcb->MessageCount > 0)
     {
+        KeAcquireSpinLock(&Fcb->MessageListLock, &oldIrql);
+        Entry = RemoveHeadList(&Fcb->MessageListHead);
+        KeReleaseSpinLock(&Fcb->MessageListLock, oldIrql);
+
         /* copy current message into buffer */
-        Message = CONTAINING_RECORD(Fcb->MessageListHead.Flink,
-                                    MSFS_MESSAGE,
-                                    MessageListEntry);
-
+        Message = CONTAINING_RECORD(Entry, MSFS_MESSAGE, MessageListEntry);
         memcpy(Buffer, &Message->Buffer, min(Message->Size,Length));
         LengthRead = Message->Size;
-
-        KeAcquireSpinLock(&Fcb->MessageListLock, &oldIrql);
-        RemoveHeadList(&Fcb->MessageListHead);
-        KeReleaseSpinLock(&Fcb->MessageListLock, oldIrql);
 
         ExFreePoolWithTag(Message, 'rFsM');
         Fcb->MessageCount--;