sys: FspFsvolDeviceInsertContext: can no longer fail because of low memory

src/sys/create.c

@@ -346,6 +346,20 @@ VOID FspFsvolCreateComplete(
 {
     FSP_ENTER_IOC(PAGED_CODE());
 
+    /*
+     * NOTE:
+     * In the following we may have to close the just opened file object. But we must
+     * never close a file we just created, because this will leave an orphan file on
+     * the disk.
+     *
+     * Files may have to be closed if a security access or share access check fails. In
+     * both those cases we were opening an existing file and so it is safe to close it.
+     *
+     * Because of how IRP_MJ_CREATE works in Windows, it is difficult to improve on this
+     * scheme without introducing a 2-phase Create protocol, which is undesirable as it
+     * means two trips into user-mode for a single Create request.
+     */
+
     PDEVICE_OBJECT DeviceObject = IrpSp->DeviceObject;
     FSP_FSVOL_DEVICE_EXTENSION *FsvolDeviceExtension = FspFsvolDeviceExtension(DeviceObject);
     FSP_FSVRT_DEVICE_EXTENSION *FsvrtDeviceExtension =
@@ -400,11 +414,11 @@ VOID FspFsvolCreateComplete(
                     goto reparse_fail;
                 }
                 ExFreePool(FileObject->FileName.Buffer);
-                FileObject->FileName.Length = 0;
                 FileObject->FileName.MaximumLength = ReparseFileName.Length;
                 FileObject->FileName.Buffer = Buffer;
-                RtlCopyUnicodeString(&FileObject->FileName, &ReparseFileName);
             }
+            FileObject->FileName.Length = 0;
+            RtlCopyUnicodeString(&FileObject->FileName, &ReparseFileName);
         }
         else
         if (IO_REMOUNT == Response->IoStatus.Information)
@@ -471,13 +485,11 @@ VOID FspFsvolCreateComplete(
     ExAcquireResourceExclusiveLite(&FsvolDeviceExtension->Base.Resource, TRUE);
     try
     {
-        /* attempt to insert the newly created FsContext into our generic table */
+        /* insert the newly created FsContext into our generic table */
         FsContext = FspFsvolDeviceInsertContext(DeviceObject,
-            FsContext->UserContext, FsContext, &Inserted);
+            FsContext->UserContext, FsContext, &FsContext->ElementStorage, &Inserted);
-        if (0 == FsContext)
+        ASSERT(0 != FsContext);
-            Result = STATUS_INSUFFICIENT_RESOURCES;
+
-        else
-        {
         /* share access check */
         if (Inserted)
         {
@@ -505,9 +517,11 @@ VOID FspFsvolCreateComplete(
                 Result = IoCheckShareAccess(AccessState->PreviouslyGrantedAccess,
                     ShareAccess, FileObject, &FsContext->ShareAccess, TRUE);
             if (NT_SUCCESS(Result))
+            {
+                FspFileContextRetain(FsContext);
                 FspFileContextOpen(FsContext);
-                ExReleaseResourceLite(FsContext->Header.Resource);
             }
+            ExReleaseResourceLite(FsContext->Header.Resource);
         }
     }
     finally
@@ -515,7 +529,7 @@ VOID FspFsvolCreateComplete(
         ExReleaseResourceLite(&FsvolDeviceExtension->Base.Resource);
     }
 
-    /* did we fail to insert? */
+    /* did we fail our share access checks? */
     if (!NT_SUCCESS(Result))
     {
         ASSERT(!Inserted);

src/sys/device.c

@@ -26,7 +26,7 @@ VOID FspFsctlDeviceVolumeCreated(PDEVICE_OBJECT DeviceObject);
 VOID FspFsctlDeviceVolumeDeleted(PDEVICE_OBJECT DeviceObject);
 PVOID FspFsvolDeviceLookupContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier);
 PVOID FspFsvolDeviceInsertContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier, PVOID Context,
-    PBOOLEAN PInserted);
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT *ElementStorage, PBOOLEAN PInserted);
 VOID FspFsvolDeviceDeleteContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier,
     PBOOLEAN PDeleted);
 static RTL_AVL_COMPARE_ROUTINE FspFsvolDeviceCompareElement;
@@ -61,12 +61,6 @@ VOID FspDeviceDeleteAll(VOID);
 #pragma alloc_text(PAGE, FspDeviceDeleteAll)
 #endif
 
-typedef struct
-{
-    UINT64 Identifier;
-    PVOID Context;
-} FSP_DEVICE_GENERIC_TABLE_ELEMENT;
-
 NTSTATUS FspDeviceCreateSecure(UINT32 Kind, ULONG ExtraSize,
     PUNICODE_STRING DeviceName, DEVICE_TYPE DeviceType,
     PUNICODE_STRING DeviceSddl, LPCGUID DeviceClassGuid,
@@ -236,7 +230,7 @@ static VOID FspFsvolDeviceFini(PDEVICE_OBJECT DeviceObject)
      * Enumerate and delete all entries in the GenericTable.
      * There is no need to protect accesses to the table as we are in the device destructor.
      */
-    FSP_DEVICE_GENERIC_TABLE_ELEMENT *Element;
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT_DATA *Element;
     while (0 != (Element = RtlGetElementGenericTableAvl(&FsvolDeviceExtension->GenericTable, 0)))
         RtlDeleteElementGenericTableAvl(&FsvolDeviceExtension->GenericTable, &Element->Identifier);
 
@@ -318,7 +312,7 @@ PVOID FspFsvolDeviceLookupContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier
     ASSERT(FspFsvolDeviceExtensionKind == FsvolDeviceExtension->Base.Kind);
     ASSERT(ExIsResourceAcquiredExclusiveLite(&FsvolDeviceExtension->Base.Resource));
 
-    FSP_DEVICE_GENERIC_TABLE_ELEMENT *Result;
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT_DATA *Result;
 
     Result = RtlLookupElementGenericTableAvl(&FsvolDeviceExtension->GenericTable, &Identifier);
 
@@ -326,7 +320,7 @@ PVOID FspFsvolDeviceLookupContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier
 }
 
 PVOID FspFsvolDeviceInsertContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier, PVOID Context,
-    PBOOLEAN PInserted)
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT *ElementStorage, PBOOLEAN PInserted)
 {
     PAGED_CODE();
 
@@ -334,12 +328,14 @@ PVOID FspFsvolDeviceInsertContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier
     ASSERT(FspFsvolDeviceExtensionKind == FsvolDeviceExtension->Base.Kind);
     ASSERT(ExIsResourceAcquiredExclusiveLite(&FsvolDeviceExtension->Base.Resource));
 
-    FSP_DEVICE_GENERIC_TABLE_ELEMENT *Result, Element = { 0 };
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT_DATA *Result, Element = { 0 };
     Element.Identifier = Identifier;
     Element.Context = Context;
 
+    FsvolDeviceExtension->GenericTableElementStorage = ElementStorage;
     Result = RtlInsertElementGenericTableAvl(&FsvolDeviceExtension->GenericTable,
         &Element, sizeof Element, PInserted);
+    FsvolDeviceExtension->GenericTableElementStorage = 0;
 
     return 0 != Result ? Result->Context : 0;
 }
@@ -380,15 +376,18 @@ static PVOID NTAPI FspFsvolDeviceAllocateElement(
 {
     PAGED_CODE();
 
-    return ExAllocatePoolWithTag(PagedPool, ByteSize, FSP_TAG);
+    FSP_FSVOL_DEVICE_EXTENSION *FsvolDeviceExtension =
+        CONTAINING_RECORD(Table, FSP_FSVOL_DEVICE_EXTENSION, GenericTable);
+
+    ASSERT(sizeof(FSP_DEVICE_GENERIC_TABLE_ELEMENT) == ByteSize);
+
+    return FsvolDeviceExtension->GenericTableElementStorage;
 }
 
 static VOID NTAPI FspFsvolDeviceFreeElement(
     PRTL_AVL_TABLE Table, PVOID Buffer)
 {
     PAGED_CODE();
-
-    ExFreePoolWithTag(Buffer, FSP_TAG);
 }
 
 NTSTATUS FspDeviceCopyList(

src/sys/driver.h

@@ -305,7 +305,18 @@ typedef struct
     FSP_DEVICE_EXTENSION Base;
     PDEVICE_OBJECT FsvrtDeviceObject;
     RTL_AVL_TABLE GenericTable;
+    PVOID GenericTableElementStorage;
 } FSP_FSVOL_DEVICE_EXTENSION;
+typedef struct
+{
+    UINT64 Identifier;
+    PVOID Context;
+} FSP_DEVICE_GENERIC_TABLE_ELEMENT_DATA;
+typedef struct
+{
+    RTL_BALANCED_LINKS Header;
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT_DATA Data;
+} FSP_DEVICE_GENERIC_TABLE_ELEMENT;
 static inline
 FSP_DEVICE_EXTENSION *FspDeviceExtension(PDEVICE_OBJECT DeviceObject)
 {
@@ -343,7 +354,7 @@ VOID FspFsctlDeviceVolumeCreated(PDEVICE_OBJECT DeviceObject);
 VOID FspFsctlDeviceVolumeDeleted(PDEVICE_OBJECT DeviceObject);
 PVOID FspFsvolDeviceLookupContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier);
 PVOID FspFsvolDeviceInsertContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier, PVOID Context,
-    PBOOLEAN PInserted);
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT *ElementStorage, PBOOLEAN PInserted);
 VOID FspFsvolDeviceDeleteContext(PDEVICE_OBJECT DeviceObject, UINT64 Identifier,
     PBOOLEAN PDeleted);
 NTSTATUS FspDeviceCopyList(
@@ -370,6 +381,7 @@ typedef struct
     SHARE_ACCESS ShareAccess;
     BOOLEAN DeletePending;
     /* read-only after creation */
+    FSP_DEVICE_GENERIC_TABLE_ELEMENT ElementStorage;
     UINT64 UserContext;
     UNICODE_STRING FileName;
     WCHAR FileNameBuf[];