sys,dll: FspFileSystemResolveReparsePoints: use IO_REPARSE_TAG_SYMLINK instead of IO_REPARSE for symlink resolution

- FspFsvolCreateComplete STATUS_REPARSE handling changed to support device-relative symlink reparse points

src/dll/fsop.c

@@ -1057,6 +1057,7 @@ FSP_API NTSTATUS FspFileSystemResolveReparsePoints(FSP_FILE_SYSTEM *FileSystem,
     PWSTR FileName, UINT32 ReparsePointIndex, BOOLEAN ResolveLastPathComponent0,
     PIO_STATUS_BLOCK PIoStatus, PVOID Buffer, PSIZE_T PSize)
 {
+    PREPARSE_DATA_BUFFER OutputReparseData;
     PWSTR TargetPath, RemainderPath, LastPathComponent, NewRemainderPath, ReparseTargetPath;
     WCHAR RemainderChar;
     union
@@ -1070,10 +1071,17 @@ FSP_API NTSTATUS FspFileSystemResolveReparsePoints(FSP_FILE_SYSTEM *FileSystem,
     ULONG MaxTries = 32;
     NTSTATUS Result;
 
-    TargetPath = Buffer;
     RemainderPathSize = (lstrlenW(FileName) + 1) * sizeof(WCHAR);
-    if (RemainderPathSize > *PSize)
+    if (FIELD_OFFSET(REPARSE_DATA_BUFFER, SymbolicLinkReparseBuffer.PathBuffer) +
+        RemainderPathSize > *PSize)
         return STATUS_REPARSE_POINT_NOT_RESOLVED;
+
+    OutputReparseData = Buffer;
+    memset(OutputReparseData, 0,
+        FIELD_OFFSET(REPARSE_DATA_BUFFER, SymbolicLinkReparseBuffer.PathBuffer));
+    OutputReparseData->ReparseTag = IO_REPARSE_TAG_SYMLINK;
+    OutputReparseData->SymbolicLinkReparseBuffer.Flags = SYMLINK_FLAG_RELATIVE;
+    TargetPath = OutputReparseData->SymbolicLinkReparseBuffer.PathBuffer;
     memcpy(TargetPath, FileName, RemainderPathSize);
 
     ResolveLastPathComponent = ResolveLastPathComponent0;
@@ -1089,7 +1097,7 @@ FSP_API NTSTATUS FspFileSystemResolveReparsePoints(FSP_FILE_SYSTEM *FileSystem,
             if (L'\0' == *RemainderPath)
             {
                 if (!ResolveLastPathComponent)
-                    goto exit;
+                    goto symlink_exit;
                 ResolveLastPathComponent = FALSE;
                 break;
             }
@@ -1164,44 +1172,57 @@ FSP_API NTSTATUS FspFileSystemResolveReparsePoints(FSP_FILE_SYSTEM *FileSystem,
         if (IO_REPARSE_TAG_SYMLINK != ReparseData->ReparseTag)
             goto reparse_data_exit;
 
+        if (0 == --MaxTries)
+            return STATUS_REPARSE_POINT_NOT_RESOLVED;
+
         ReparseTargetPath = ReparseData->SymbolicLinkReparseBuffer.PathBuffer +
             ReparseData->SymbolicLinkReparseBuffer.SubstituteNameOffset / sizeof(WCHAR);
         ReparseTargetPathLength = ReparseData->SymbolicLinkReparseBuffer.SubstituteNameLength;
 
-        /* if an absolute (in the NT namespace) symlink return the full reparse point */
-        if (0 == (ReparseData->SymbolicLinkReparseBuffer.Flags & SYMLINK_FLAG_RELATIVE) &&
-            ReparseTargetPathLength >= sizeof(WCHAR) && L'\\' == ReparseTargetPath[0])
-            goto reparse_data_exit;
-
-        if (0 == --MaxTries)
-            return STATUS_REPARSE_POINT_NOT_RESOLVED;
-
         /* if device relative symlink replace whole path; else replace last path component */
         NewRemainderPath = ReparseTargetPathLength >= sizeof(WCHAR) && L'\\' == ReparseTargetPath[0] ?
             TargetPath : LastPathComponent;
 
     reparse:
         RemainderPathSize = (lstrlenW(RemainderPath) + 1) * sizeof(WCHAR);
-        if (NewRemainderPath + (ReparseTargetPathLength + RemainderPathSize) / sizeof(WCHAR) >
+        if ((PUINT8)NewRemainderPath + ReparseTargetPathLength + RemainderPathSize >
-            TargetPath + *PSize / sizeof(WCHAR))
+            (PUINT8)Buffer + *PSize)
             return STATUS_REPARSE_POINT_NOT_RESOLVED;
 
         /* move remainder path to its new position */
-        memmove(NewRemainderPath + ReparseTargetPathLength / sizeof(WCHAR),
+        memmove((PUINT8)NewRemainderPath + ReparseTargetPathLength,
             RemainderPath, RemainderPathSize);
 
         /* copy symlink target */
         memcpy(NewRemainderPath, ReparseTargetPath, ReparseTargetPathLength);
 
+        /* if an absolute (in the NT namespace) symlink exit now */
+        if (0 != ReparseTargetPath /* ensure we are not doing dot handling */ &&
+            0 == (ReparseData->SymbolicLinkReparseBuffer.Flags & SYMLINK_FLAG_RELATIVE) &&
+            ReparseTargetPathLength >= sizeof(WCHAR) && L'\\' == ReparseTargetPath[0])
+        {
+            OutputReparseData->SymbolicLinkReparseBuffer.Flags = 0;
+            goto symlink_exit;
+        }
+
         ResolveLastPathComponent = ResolveLastPathComponent0;
         RemainderPath = NewRemainderPath;
     }
 
-exit:
+symlink_exit:
-    *PSize = (PUINT8)RemainderPath - (PUINT8)TargetPath;
+    OutputReparseData->SymbolicLinkReparseBuffer.SubstituteNameLength =
+        OutputReparseData->SymbolicLinkReparseBuffer.PrintNameLength =
+        (USHORT)lstrlenW(OutputReparseData->SymbolicLinkReparseBuffer.PathBuffer) * sizeof(WCHAR);
+    OutputReparseData->ReparseDataLength =
+        FIELD_OFFSET(REPARSE_DATA_BUFFER, SymbolicLinkReparseBuffer.PathBuffer) -
+        FIELD_OFFSET(REPARSE_DATA_BUFFER, SymbolicLinkReparseBuffer) +
+        OutputReparseData->SymbolicLinkReparseBuffer.SubstituteNameLength;
+
+    *PSize = FIELD_OFFSET(REPARSE_DATA_BUFFER, SymbolicLinkReparseBuffer) +
+        OutputReparseData->ReparseDataLength;
 
     PIoStatus->Status = STATUS_REPARSE;
-    PIoStatus->Information = 0/*IO_REPARSE*/;
+    PIoStatus->Information = ReparseData->ReparseTag;
     return STATUS_REPARSE;
 
 reparse_data_exit:

src/sys/create.c

@@ -510,22 +510,24 @@ NTSTATUS FspFsvolCreateComplete(
                 IO_REPARSE_TAG_SYMLINK == Response->IoStatus.Information)
             {
                 /*
-                 * IO_REPARSE means that the user-mode file system has returned a device-relative
+                 * IO_REPARSE means that the user-mode file system has returned an absolute (in
-                 * (absolute in the device namespace) path. Prefix it with our device name/prefix
+                 * the device namespace) path. Send it as is to the IO Manager.
-                 * and send it to the IO Manager.
                  *
                  * IO_REPARSE_TAG_SYMLINK means that the user-mode file system has returned a full
-                 * symbolic link reparse buffer with an absolute (in the NT namespace) path. Send
+                 * symbolic link reparse buffer. If the symbolic link is absolute send it to the
-                 * it as is to the IO Manager. The FSD cannot handle relative symbolic links, so
+                 * IO Manager as is. If the symbolic link is device-relative (absolute in the
-                 * it is the responsibility of the user-mode file system to resolve them.
+                 * device namespace) prefix it with our volume name/prefix and then send it to the
+                 * IO Manager.
+                 *
+                 * We do our own handling of IO_REPARSE_TAG_SYMLINK reparse points because
+                 * experimentation with handling them directly to the IO Manager revealed problems
+                 * with UNC paths (\??\UNC\{VolumePrefix}\{FilePath}).
                  */
 
                 if (IO_REPARSE == Response->IoStatus.Information)
                 {
-                    RtlCopyMemory(&ReparseTargetPrefix0, &FsvolDeviceExtension->VolumeName,
+                    RtlZeroMemory(&ReparseTargetPrefix0, sizeof ReparseTargetPrefix0);
-                        sizeof ReparseTargetPrefix0);
+                    RtlZeroMemory(&ReparseTargetPrefix1, sizeof ReparseTargetPrefix1);
-                    RtlCopyMemory(&ReparseTargetPrefix1, &FsvolDeviceExtension->VolumePrefix,
-                        sizeof ReparseTargetPrefix1);
 
                     ReparseTargetPath.Length = ReparseTargetPath.MaximumLength =
                         Response->Rsp.Create.Reparse.Buffer.Size;
@@ -552,16 +554,25 @@ NTSTATUS FspFsvolCreateComplete(
                     if (!NT_SUCCESS(Result))
                         FSP_RETURN(Result = STATUS_REPARSE_POINT_NOT_RESOLVED);
 
+                    if (!FlagOn(ReparseData->SymbolicLinkReparseBuffer.Flags, SYMLINK_FLAG_RELATIVE))
+                    {
                         RtlZeroMemory(&ReparseTargetPrefix0, sizeof ReparseTargetPrefix0);
                         RtlZeroMemory(&ReparseTargetPrefix1, sizeof ReparseTargetPrefix1);
+                    }
+                    else
+                    {
+                        RtlCopyMemory(&ReparseTargetPrefix0, &FsvolDeviceExtension->VolumeName,
+                            sizeof ReparseTargetPrefix0);
+                        RtlCopyMemory(&ReparseTargetPrefix1, &FsvolDeviceExtension->VolumePrefix,
+                            sizeof ReparseTargetPrefix1);
+                    }
 
                     ReparseTargetPath.Buffer = ReparseData->SymbolicLinkReparseBuffer.PathBuffer +
                         ReparseData->SymbolicLinkReparseBuffer.SubstituteNameOffset / sizeof(WCHAR);
                     ReparseTargetPath.Length = ReparseTargetPath.MaximumLength =
                         ReparseData->SymbolicLinkReparseBuffer.SubstituteNameLength;
 
-                    if (FlagOn(ReparseData->SymbolicLinkReparseBuffer.Flags, SYMLINK_FLAG_RELATIVE) ||
+                    if (ReparseTargetPath.Length < sizeof(WCHAR) || L'\\' != ReparseTargetPath.Buffer[0])
-                        ReparseTargetPath.Length < sizeof(WCHAR) || L'\\' != ReparseTargetPath.Buffer[0])
                         FSP_RETURN(Result = STATUS_REPARSE_POINT_NOT_RESOLVED);
                 }