Fix resolving NTFS symbolic links that point to UNC shares

Without this change, the target of a symbolic link that points to a UNC
share would include UNC in the target path, and not be correctly made
absolute.

Add a relevant test case, and use the opportunity to factor out the
helper code that creates NTFS symlinks into a function that takes
care of error handling.

The file created with the new test case only gets cleaned up correctly
when passing the file path into QDir::rmdir, which is either way the
right thing to do.

[ChangeLog][QtCore][QFileInfo] Fixed resolving of symbolic links to UNC
shares on NTFS file systems.

Change-Id: I9ba75d627aedf7c4cc289f0cb71088d795d30d8a
Fixes: QTBUG-73688
Task-number: QTBUG-63970
Task-number: QTBUG-30401
Task-number: QTBUG-20791
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/corelib/io/qfilesystemengine_win.cpp b/src/corelib/io/qfilesystemengine_win.cpp
index 2020e34f93..279918b812 100644
--- a/src/corelib/io/qfilesystemengine_win.cpp
+++ b/src/corelib/io/qfilesystemengine_win.cpp
@@ -310,9 +310,18 @@ static QString readSymLink(const QFileSystemEntry &link)
                 const wchar_t* PathBuffer = &rdb->SymbolicLinkReparseBuffer.PathBuffer[offset];
                 result = QString::fromWCharArray(PathBuffer, length);
             }
-            // cut-off "//?/" and "/??/"
-            if (result.size() > 4 && result.at(0) == QLatin1Char('\\') && result.at(2) == QLatin1Char('?') && result.at(3) == QLatin1Char('\\'))
+            // cut-off "\\?\" and "\??\"
+            if (result.size() > 4
+                    && result.at(0) == QLatin1Char('\\')
+                    && result.at(2) == QLatin1Char('?')
+                    && result.at(3) == QLatin1Char('\\')) {
                 result = result.mid(4);
+                // cut off UNC in addition when the link points at a UNC share
+                // in which case we need to prepend another backslash to get \\server\share
+                if (result.leftRef(3) == QLatin1String("UNC")) {
+                    result.replace(0, 3, QLatin1Char('\\'));
+                }
+            }
         }
         free(rdb);
         CloseHandle(handle);