Fix QDir::mkpath() when the path contains "symlink/../"

It is incorrect to collapse a "symlink/.." segment because the parent
directory of the symlink's target may not be the directory where the
symlink itself is located.

[ChangeLog][QtCore][QDir] Fixed a bug that caused QDir::mkpath() to
create the wrong directory if the requested path contained a symbolic
link and "../".

Change-Id: Iaddbecfbba5441c8b2e4fffd14a3e367730a1e24
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/io/qfilesystemengine_unix.cpp

@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2017 Intel Corporation.
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Copyright (C) 2013 Samuel Gaist <samuel.gaist@edeltech.ch>
 ** Contact: https://www.qt.io/licensing/
@@ -603,25 +604,7 @@ bool QFileSystemEngine::createDirectory(const QFileSystemEntry &entry, bool crea
     if (!createParents)
         return false;
 
-    // we need the cleaned path in order to create the parents
-    // and we save errno just in case encodeName needs to load codecs
-    int savedErrno = errno;
-    bool pathChanged;
-    {
-        QString cleanName = QDir::cleanPath(dirName);
-
-        // Check if the cleaned name is the same or not. If we were given a
-        // path with resolvable "../" sections, cleanPath will remove them, but
-        // this may change the target dir if one of those segments was a
-        // symlink. This operation depends on cleanPath's optimization of
-        // returning the original string if it didn't modify anything.
-        pathChanged = !dirName.isSharedWith(cleanName);
-        if (pathChanged)
-            nativeName = QFile::encodeName(cleanName);
-    }
-
-    errno = savedErrno;
-    return createDirectoryWithParents(nativeName, pathChanged);
+    return createDirectoryWithParents(nativeName, false);
 }
 
 //static

tests/auto/corelib/io/qdir/tst_qdir.cpp

@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2017 Intel Corporation.
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -101,6 +102,7 @@ private slots:
 
     void mkdirRmdir_data();
     void mkdirRmdir();
+    void mkdirOnSymlink();
 
     void makedirReturnCode();
 
@@ -387,6 +389,56 @@ void tst_QDir::mkdirRmdir()
     QVERIFY(!fi.exists());
 }
 
+void tst_QDir::mkdirOnSymlink()
+{
+#ifndef Q_OS_UNIX
+    QSKIP("Test only valid on an OS that supports symlinks");
+#else
+    // Create the structure:
+    //    .
+    //    ├── symlink -> two/three
+    //    └── two
+    //        └── three
+    // so when we mkdir("symlink/../four/five"), we end up with:
+    //    .
+    //    ├── symlink -> two/three
+    //    └── two
+    //        ├── four
+    //        │   └── five
+    //        └── three
+
+    QDir dir;
+    struct Clean {
+        QDir &dir;
+        Clean(QDir &dir) : dir(dir) {}
+        ~Clean() { doClean(); }
+        void doClean() {
+            dir.rmpath("two/three");
+            dir.rmpath("two/four/five");
+            // in case the test fails, don't leave junk behind
+            dir.rmpath("four/five");
+            QFile::remove("symlink");
+        }
+    };
+    Clean clean(dir);
+    clean.doClean();
+
+    // create our structure:
+    dir.mkpath("two/three");
+    ::symlink("two/three", "symlink");
+
+    // try it:
+    QString path = "symlink/../four/five";
+    QVERIFY(dir.mkpath(path));
+    QFileInfo fi(path);
+    QVERIFY2(fi.exists() && fi.isDir(), msgDoesNotExist(path).constData());
+
+    path = "two/four/five";
+    fi.setFile(path);
+    QVERIFY2(fi.exists() && fi.isDir(), msgDoesNotExist(path).constData());
+#endif
+}
+
 void tst_QDir::makedirReturnCode()
 {
     QString dirName = QString::fromLatin1("makedirReturnCode");