From 7eefe702949da68e49c4365d466c5373099c3b1f Mon Sep 17 00:00:00 2001
From: Pierre Schweitzer <pierre@reactos.org>
Date: Sun, 12 Nov 2017 22:26:18 +0100
Subject: [PATCH] [NTOSKRNL] Implement IoComputeDesiredAccessFileObject() based
 on checks performed in NtFlushBuffersFile() CORE-14003

---
 ntoskrnl/include/internal/io.h |  7 +++++++
 ntoskrnl/io/iomgr/util.c       | 27 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/ntoskrnl/include/internal/io.h b/ntoskrnl/include/internal/io.h
index 54a46906db1..2a4c62f42d1 100644
--- a/ntoskrnl/include/internal/io.h
+++ b/ntoskrnl/include/internal/io.h
@@ -1230,6 +1230,13 @@ IopDoNameTransmogrify(
     IN PREPARSE_DATA_BUFFER DataBuffer
 );
 
+NTSTATUS
+NTAPI
+IoComputeDesiredAccessFileObject(
+    IN PFILE_OBJECT FileObject,
+    IN PACCESS_MASK DesiredAccess
+);
+
 //
 // I/O Timer Routines
 //
diff --git a/ntoskrnl/io/iomgr/util.c b/ntoskrnl/io/iomgr/util.c
index 14bfafda7c3..7329dbf8f10 100644
--- a/ntoskrnl/io/iomgr/util.c
+++ b/ntoskrnl/io/iomgr/util.c
@@ -19,6 +19,33 @@ NTAPI
 RtlpGetStackLimits(PULONG_PTR StackBase,
                    PULONG_PTR StackLimit);
 
+/* PRIVATE FUNCTIONS *********************************************************/
+
+NTSTATUS
+NTAPI
+IoComputeDesiredAccessFileObject(IN PFILE_OBJECT FileObject,
+                                 IN PACCESS_MASK DesiredAccess)
+{
+    /* Assume failure */
+    *DesiredAccess = 0;
+
+    /* First check we really have a FileObject */
+    if (OBJECT_TO_OBJECT_HEADER(FileObject)->Type != IoFileObjectType)
+    {
+        return STATUS_OBJECT_TYPE_MISMATCH;
+    }
+
+    /* Then compute desired access:
+     * Check if the handle has either FILE_WRITE_DATA or FILE_APPEND_DATA was
+     * granted. However, if this is a named pipe, make sure we don't ask for
+     * FILE_APPEND_DATA as it interferes with the FILE_CREATE_PIPE_INSTANCE
+     * access right!
+     */
+    *DesiredAccess = ((!(FileObject->Flags & FO_NAMED_PIPE) ? FILE_APPEND_DATA : 0) | FILE_WRITE_DATA);
+
+    return STATUS_SUCCESS;
+}
+
 /* FUNCTIONS *****************************************************************/
 
 /*