From de83c4d4b4d9f759c840cad3ee7075912944b5d1 Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Wed, 17 Feb 2016 15:06:19 -0500
Subject: [PATCH] SystemTools: support deleting junction points

Junction points can exist in directories which may be manipulated within
CMake. The problem is that junction points are currently completely
unsupported within CMake. Since junctions need special API calls to
manipulate, DeleteFileW does not work and instead DeviceIoControl must
be used. Token privilege API calls must also be used to be able to
actually open the junction points.

Change-Id: I3e4ff3b7a600146ac3574d2b17890eef07d06496
---
 SystemTools.cxx | 106 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)

diff --git a/SystemTools.cxx b/SystemTools.cxx
index 3d8c79ab..544a638c 100644
--- a/SystemTools.cxx
+++ b/SystemTools.cxx
@@ -35,6 +35,7 @@
 #include <fstream>
 #include <sstream>
 #include <set>
+#include <vector>
 
 // Work-around CMake dependency scanning limitation.  This must
 // duplicate the above list of headers.
@@ -88,6 +89,7 @@
 // Windows API.
 #if defined(_WIN32)
 # include <windows.h>
+# include <winioctl.h>
 # ifndef INVALID_FILE_ATTRIBUTES
 #  define INVALID_FILE_ATTRIBUTES ((DWORD)-1)
 # endif
@@ -2755,6 +2757,106 @@ std::string SystemTools::GetLastSystemError()
   return strerror(e);
 }
 
+#ifdef _WIN32
+
+static bool IsJunction(const std::wstring& source)
+{
+#ifdef FSCTL_GET_REPARSE_POINT
+  const DWORD JUNCTION_ATTRS = FILE_ATTRIBUTE_DIRECTORY |
+                               FILE_ATTRIBUTE_REPARSE_POINT;
+  DWORD attrs = GetFileAttributesW(source.c_str());
+  if (attrs == INVALID_FILE_ATTRIBUTES)
+    {
+    return false;
+    }
+  if ((attrs & JUNCTION_ATTRS) != JUNCTION_ATTRS)
+    {
+    return false;
+    }
+
+  // Adjust privileges so that we can succefully open junction points.
+  HANDLE token;
+  TOKEN_PRIVILEGES privs;
+  OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES, &token);
+  LookupPrivilegeValue(NULL, SE_BACKUP_NAME, &privs.Privileges[0].Luid);
+  privs.PrivilegeCount = 1;
+  privs.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
+  AdjustTokenPrivileges(token, FALSE, &privs, sizeof(TOKEN_PRIVILEGES), NULL, NULL);
+  CloseHandle(token);
+
+  HANDLE dir = CreateFileW(source.c_str(), GENERIC_READ,
+                           0, NULL, OPEN_EXISTING,
+                           FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, NULL);
+  if (dir == INVALID_HANDLE_VALUE)
+    {
+    return false;
+    }
+
+  // Query whether this is a reparse point or not.
+  BYTE buffer[MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
+  REPARSE_GUID_DATA_BUFFER *reparse_buffer =
+    (REPARSE_GUID_DATA_BUFFER*) buffer;
+  DWORD sentinel;
+
+  BOOL success = DeviceIoControl(
+    dir, FSCTL_GET_REPARSE_POINT,
+    NULL, 0,
+    reparse_buffer, MAXIMUM_REPARSE_DATA_BUFFER_SIZE,
+    &sentinel, NULL);
+
+  CloseHandle(dir);
+
+  return (success && (reparse_buffer->ReparseTag == IO_REPARSE_TAG_MOUNT_POINT));
+#else
+  return false;
+#endif
+}
+
+static bool DeleteJunction(const std::wstring& source)
+{
+#ifdef FSCTL_DELETE_REPARSE_POINT
+  // Adjust privileges so that we can succefully open junction points as
+  // read/write.
+  HANDLE token;
+  TOKEN_PRIVILEGES privs;
+  OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES, &token);
+  LookupPrivilegeValue(NULL, SE_RESTORE_NAME, &privs.Privileges[0].Luid);
+  privs.PrivilegeCount = 1;
+  privs.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
+  AdjustTokenPrivileges(token, FALSE, &privs, sizeof(TOKEN_PRIVILEGES), NULL, NULL);
+  CloseHandle(token);
+
+  HANDLE dir = CreateFileW(source.c_str(), GENERIC_READ | GENERIC_WRITE,
+                           0, NULL, OPEN_EXISTING,
+                           FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, NULL);
+  if (dir == INVALID_HANDLE_VALUE)
+    {
+    return false;
+    }
+
+  // Set up the structure so that we can delete the junction.
+  std::vector<BYTE> buffer(REPARSE_GUID_DATA_BUFFER_HEADER_SIZE, 0);
+  REPARSE_GUID_DATA_BUFFER *reparse_buffer =
+    (REPARSE_GUID_DATA_BUFFER*) &buffer[0];
+  DWORD sentinel;
+
+  reparse_buffer->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
+
+  BOOL success = DeviceIoControl(
+    dir, FSCTL_DELETE_REPARSE_POINT,
+    reparse_buffer, REPARSE_GUID_DATA_BUFFER_HEADER_SIZE,
+    NULL, 0,
+    &sentinel, NULL);
+
+  CloseHandle(dir);
+
+  return !!success;
+#else
+  return false;
+#endif
+}
+#endif
+
 bool SystemTools::RemoveFile(const std::string& source)
 {
 #ifdef _WIN32
@@ -2782,6 +2884,10 @@ bool SystemTools::RemoveFile(const std::string& source)
     SetLastError(err);
     return false;
     }
+  if (IsJunction(ws) && !DeleteJunction(ws))
+    {
+    return false;
+    }
   if (DeleteFileW(ws.c_str()) ||
       GetLastError() == ERROR_FILE_NOT_FOUND ||
       GetLastError() == ERROR_PATH_NOT_FOUND)
-- 
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