QStandardPaths/Unix: improve the XDG_RUNTIME_DIR creation/detection

First, use QT_MKDIR instead of QFileSystemEngine::createDirectory(), as
the latter can't create a directory with the right permissions. That
would allow an attacker to briefly obtain access to the runtime dir
between the mkdir() and chmod() system calls.

Second, make sure that if the target already exists that it is a
directory and not a symlink (even to a directory). If it is a symlink
that belongs to another user, it can be changed to point to another
place, which we won't like.

And as a bonus, we're printing more information to the user in case
something went wrong. Sample outputs:

 QStandardPaths: runtime directory '/root' is not owned by UID 1000, but a directory permissions 0700 owned by UID 0 GID 0

 QStandardPaths: runtime directory '/dev/null' is not a directory, but a character device, socket or FIFO permissions 0666 owned by UID 0 GID 0

 QStandardPaths: runtime directory '/etc/passwd' is not a directory, but a regular file permissions 0644 owned by UID 0 GID 0

 QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-tjmaciei'
 QStandardPaths: runtime directory '/tmp/runtime-tjmaciei' is not a directory, but a symbolic link to a directory permissions 0755 owned by UID 1000 GID 100

Pick-to: 5.15 5.12 5.9
Change-Id: Iea47e0f8fc8b40378df7fffd16248b663794c613
Reviewed-by: David Faure <david.faure@kdab.com>

2 files changed, 204 insertions, 59 deletions

diff --git a/tests/auto/corelib/io/qstandardpaths/qstandardpaths.pro b/tests/auto/corelib/io/qstandardpaths/qstandardpaths.pro
index 44b1ce8dd8..5c15ad84be 100644
--- a/tests/auto/corelib/io/qstandardpaths/qstandardpaths.pro
+++ b/tests/auto/corelib/io/qstandardpaths/qstandardpaths.pro
@@ -1,8 +1,6 @@
 CONFIG += testcase
 TARGET = tst_qstandardpaths
 QT = core testlib
-INCLUDEPATH += ../../../../shared/
-HEADERS += ../../../../shared/emulationdetector.h
 SOURCES = tst_qstandardpaths.cpp
 TESTDATA += tst_qstandardpaths.cpp qstandardpaths.pro
 
diff --git a/tests/auto/corelib/io/qstandardpaths/tst_qstandardpaths.cpp b/tests/auto/corelib/io/qstandardpaths/tst_qstandardpaths.cpp
index cba7dfe9fc..16b4fb4423 100644
--- a/tests/auto/corelib/io/qstandardpaths/tst_qstandardpaths.cpp
+++ b/tests/auto/corelib/io/qstandardpaths/tst_qstandardpaths.cpp
@@ -1,6 +1,7 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
+** Copyright (C) 2020 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -26,13 +27,13 @@
 **
 ****************************************************************************/
 
-#include <QtTest/QtTest>
 #include <qstandardpaths.h>
+#include <QtTest/QtTest>
 #include <qdebug.h>
-#include <qstandardpaths.h>
 #include <qfileinfo.h>
-#include <qsysinfo.h>
+#include <qplatformdefs.h>
 #include <qregularexpression.h>
+#include <qsysinfo.h>
 #if defined(Q_OS_WIN)
 #  include <qt_windows.h>
 #endif
@@ -40,14 +41,13 @@
 #ifdef Q_OS_UNIX
 #include <unistd.h>
 #include <sys/types.h>
+#include <pwd.h>
 #endif
 
 #if defined(Q_OS_UNIX) && !defined(Q_OS_MAC) && !defined(Q_OS_ANDROID)
 #define Q_XDG_PLATFORM
 #endif
 
-#include "emulationdetector.h"
-
 // Update this when adding new enum values; update enumNames too
 static const int MaxStandardLocation = QStandardPaths::AppConfigLocation;
 
@@ -68,6 +68,7 @@ private slots:
     void testFindExecutable();
     void testFindExecutableLinkToDirectory();
     void testRuntimeDirectory();
+    void testCustomRuntimeDirectory_data();
     void testCustomRuntimeDirectory();
     void testAllWritableLocations_data();
     void testAllWritableLocations();
@@ -455,6 +456,9 @@ void tst_qstandardpaths::testFindExecutableLinkToDirectory()
     QFile::remove(target);
 }
 
+using RuntimeDirSetup = QString (*)(QDir &);
+Q_DECLARE_METATYPE(RuntimeDirSetup);
+
 void tst_qstandardpaths::testRuntimeDirectory()
 {
 #ifdef Q_XDG_PLATFORM
@@ -463,6 +467,174 @@ void tst_qstandardpaths::testRuntimeDirectory()
 #endif
 }
 
+#ifdef Q_XDG_PLATFORM
+static QString fallbackXdgRuntimeDir()
+{
+    static QString username = [] {
+        struct passwd *pw = getpwuid(geteuid());
+        return QString::fromLocal8Bit(pw->pw_name);
+    }();
+
+    // QDir::temp() might change from call to call
+    return QDir::temp().filePath("runtime-" + username);
+}
+#endif
+
+static QString updateRuntimeDir(const QString &path)
+{
+    qputenv("XDG_RUNTIME_DIR", QFile::encodeName(path));
+    return path;
+}
+
+static void clearRuntimeDir()
+{
+    qunsetenv("XDG_RUNTIME_DIR");
+#ifdef Q_XDG_PLATFORM
+#ifndef Q_OS_WASM
+    QTest::ignoreMessage(QtWarningMsg,
+                         qPrintable("QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '"
+                                    + fallbackXdgRuntimeDir() + '\''));
+#endif
+#endif
+}
+
+void tst_qstandardpaths::testCustomRuntimeDirectory_data()
+{
+#if defined(Q_XDG_PLATFORM)
+    QTest::addColumn<RuntimeDirSetup>("setup");
+    auto addRow = [](const char *name, RuntimeDirSetup f) {
+        QTest::newRow(name) << f;
+    };
+
+
+#  if defined(Q_OS_UNIX)
+    if (::getuid() == 0)
+        QSKIP("Running this test as root doesn't make sense");
+#  endif
+
+    addRow("environment:non-existing", [](QDir &d) {
+        return updateRuntimeDir(d.filePath("runtime"));
+    });
+
+    addRow("environment:existing", [](QDir &d) {
+        QString p = d.filePath("runtime");
+        d.mkdir("runtime");
+        QFile::setPermissions(p, QFile::ReadOwner | QFile::WriteOwner | QFile::ExeOwner);
+        return updateRuntimeDir(p);
+    });
+
+    addRow("environment-to-existing-wrong-perm", [](QDir &d) {
+        QString p = d.filePath("runtime");
+        d.mkdir("runtime");
+        QFile::setPermissions(p, QFile::ReadOwner | QFile::WriteOwner | QFile::ExeOwner |
+                                 QFile::ExeGroup | QFile::ExeOther);
+        return updateRuntimeDir(p);
+    });
+
+    addRow("environment:wrong-owner", [](QDir &) {
+        QT_STATBUF st;
+        QT_STAT("/", &st);
+
+        updateRuntimeDir("/");
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '/' is not owned by UID "
+                                     "%1, but a directory permissions %2 owned by UID %3 GID %4")
+                             .arg(getuid())
+                             .arg(st.st_mode & 07777, 4, 8, QChar('0'))
+                             .arg(st.st_uid)
+                             .arg(st.st_gid).toLatin1());
+        return fallbackXdgRuntimeDir();
+    });
+
+    addRow("environment:file", [](QDir &d) {
+        QString p = d.filePath("file");
+        QFile f(p);
+        f.open(QIODevice::WriteOnly);
+        f.setPermissions(QFile::ReadOwner | QFile::WriteOwner);
+
+        updateRuntimeDir(p);
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a regular file permissions 0600 owned by UID %2 GID %3")
+                             .arg(p).arg(getuid()).arg(getgid()).toLatin1());
+        return fallbackXdgRuntimeDir();
+    });
+
+    addRow("environment:broken-symlink", [](QDir &d) {
+        QString p = d.filePath("link");
+        QFile::link(d.filePath("this-goes-nowhere"), p);
+        updateRuntimeDir(p);
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a broken symlink")
+                             .arg(p).toLatin1());
+        return fallbackXdgRuntimeDir();
+    });
+
+    addRow("environment:symlink-to-dir", [](QDir &d) {
+        QString p = d.filePath("link");
+        d.mkdir("dir");
+        QFile::link(d.filePath("dir"), p);
+        QFile::setPermissions(p, QFile::ReadOwner | QFile::WriteOwner | QFile::ExeOwner);
+        updateRuntimeDir(p);
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a symbolic link to a directory permissions 0700 owned by UID %2 GID %3")
+                             .arg(p).arg(getuid()).arg(getgid()).toLatin1());
+        return fallbackXdgRuntimeDir();
+    });
+
+    addRow("no-environment:non-existing", [](QDir &) {
+        clearRuntimeDir();
+        return fallbackXdgRuntimeDir();
+    });
+
+    addRow("no-environment:existing", [](QDir &d) {
+        clearRuntimeDir();
+        QString p = fallbackXdgRuntimeDir();
+        d.mkdir(p);         // probably has wrong permissions
+        return p;
+    });
+
+    addRow("no-environment:fallback-is-file", [](QDir &) {
+        QString p = fallbackXdgRuntimeDir();
+        QFile f(p);
+        f.open(QIODevice::WriteOnly);
+        f.setPermissions(QFile::ReadOwner | QFile::WriteOwner);
+
+        clearRuntimeDir();
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a regular file permissions 0600 owned by UID %2 GID %3")
+                             .arg(p).arg(getuid()).arg(getgid()).toLatin1());
+        return QString();
+    });
+
+    addRow("environment-and-fallback-are-files", [](QDir &d) {
+        QString p = d.filePath("file1");
+        QFile f(p);
+        f.open(QIODevice::WriteOnly);
+        f.setPermissions(QFile::ReadOwner | QFile::WriteOwner | QFile::ReadGroup);
+        updateRuntimeDir(p);
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a regular file permissions 0640 owned by UID %2 GID %3")
+                             .arg(p).arg(getuid()).arg(getgid()).toLatin1());
+
+        f.close();
+        f.setFileName(fallbackXdgRuntimeDir());
+        f.open(QIODevice::WriteOnly);
+        f.setPermissions(QFile::ReadOwner | QFile::WriteOwner | QFile::ReadGroup);
+        QTest::ignoreMessage(QtWarningMsg,
+                             QString("QStandardPaths: runtime directory '%1' is not a directory, "
+                                     "but a regular file permissions 0640 owned by UID %2 GID %3")
+                             .arg(f.fileName()).arg(getuid()).arg(getgid()).toLatin1());
+
+        return QString();
+    });
+#endif
+}
+
 void tst_qstandardpaths::testCustomRuntimeDirectory()
 {
 #if defined(Q_OS_UNIX)
@@ -473,63 +645,38 @@ void tst_qstandardpaths::testCustomRuntimeDirectory()
 #ifdef Q_XDG_PLATFORM
     struct EnvVarRestorer
     {
-        EnvVarRestorer() : origRuntimeDir(qgetenv("XDG_RUNTIME_DIR")) {}
-        ~EnvVarRestorer() { qputenv("XDG_RUNTIME_DIR", origRuntimeDir.constData()); }
-        const QByteArray origRuntimeDir;
+        ~EnvVarRestorer()
+        {
+            qputenv("XDG_RUNTIME_DIR", origRuntimeDir);
+            qputenv("TMPDIR", origTempDir);
+        }
+        const QByteArray origRuntimeDir = qgetenv("XDG_RUNTIME_DIR");
+        const QByteArray origTempDir = qgetenv("TMPDIR");
     };
     EnvVarRestorer restorer;
 
-    // When $XDG_RUNTIME_DIR points to a directory with wrong ownership, QStandardPaths should warn
-    QByteArray rootOwnedFileName = "/tmp";
-    if (EmulationDetector::isRunningArmOnX86()) {
-        // Directory "tmp" under toolchain sysroot is detected by qemu and has same uid as current user.
-        // Try /opt instead, it might not be located in the sysroot.
-        QFileInfo rootOwnedFile = QFileInfo(QString::fromLatin1(rootOwnedFileName));
-        if (rootOwnedFile.ownerId() == ::geteuid()) {
-            rootOwnedFileName = "/opt";
-        }
-    }
-    qputenv("XDG_RUNTIME_DIR", QFile::encodeName(rootOwnedFileName));
+    // set up the environment to point to a place we control
+    QTemporaryDir tempDir;
+    QVERIFY2(tempDir.isValid(), qPrintable(tempDir.errorString()));
 
-    // It's very unlikely that /tmp is 0600 or that we can chmod it
-    // The call below outputs
-    //   "QStandardPaths: wrong ownership on runtime directory /tmp, 0 instead of $UID"
-    // but we can't reliably expect that it's owned by uid 0, I think.
-    const uid_t uid = geteuid();
-    QTest::ignoreMessage(QtWarningMsg,
-            qPrintable(QString::fromLatin1("QStandardPaths: wrong ownership on runtime directory " + rootOwnedFileName + ", 0 instead of %1").arg(uid)));
-    const QString runtimeDir = QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
-    QVERIFY2(runtimeDir.isEmpty(), qPrintable(runtimeDir));
+    QDir d(tempDir.path());
+    qputenv("TMPDIR", QFile::encodeName(tempDir.path()));
 
-    // When $XDG_RUNTIME_DIR points to a directory with wrong permissions, QStandardPaths should warn
-    const QByteArray wrongPermissionFileName = "wrong_permissions";
-    QDir::current().mkdir(wrongPermissionFileName);
-    QFile wrongPermissionFile(wrongPermissionFileName);
-    const QFile::Permissions wantedPerms = QFile::ReadUser | QFile::WriteUser | QFile::ExeUser;
-    QVERIFY(wrongPermissionFile.setPermissions(wantedPerms | QFile::ExeGroup));
+    QFETCH(RuntimeDirSetup, setup);
+    QString expected = setup(d);
 
-    qputenv("XDG_RUNTIME_DIR", wrongPermissionFileName);
-    QTest::ignoreMessage(QtWarningMsg,
-           qPrintable(QString::fromLatin1("QStandardPaths: wrong permissions on runtime directory " + wrongPermissionFileName + ", 7710 instead of 7700")));
-    const QString wrongPermissionRuntimeDir = QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
-    QVERIFY(wrongPermissionRuntimeDir.isEmpty());
-    QDir::current().rmdir(wrongPermissionFileName);
-
-    // When $XDG_RUNTIME_DIR points to a non-existing directory, QStandardPaths should create it first
-    const QByteArray nonExistingDir = "does_not_exist";
-    qputenv("XDG_RUNTIME_DIR", nonExistingDir);
-    const QString nonExistingRuntimeDir = QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
-    QVERIFY2(!nonExistingRuntimeDir.compare(nonExistingDir), qPrintable(nonExistingRuntimeDir));
-    QVERIFY(QDir::current().exists(nonExistingRuntimeDir));
-    QDir::current().rmdir(nonExistingRuntimeDir);
-
-    // When $XDG_RUNTIME_DIR points to a file, QStandardPaths should warn
-    const QString file = QFINDTESTDATA("tst_qstandardpaths.cpp");
-    QVERIFY(!file.isEmpty());
-    qputenv("XDG_RUNTIME_DIR", QFile::encodeName(file));
-    QTest::ignoreMessage(QtWarningMsg, qPrintable(QString::fromLatin1("QStandardPaths: XDG_RUNTIME_DIR points to '%1' which is not a directory").arg(file)));
-    const QString noRuntimeDir = QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
-    QVERIFY2(noRuntimeDir.isEmpty(), qPrintable(file));
+    QString runtimeDir = QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
+    QCOMPARE(runtimeDir, expected);
+
+    if (!runtimeDir.isEmpty()) {
+        QFileInfo runtimeInfo(runtimeDir);
+        QVERIFY(runtimeInfo.isDir());
+        QVERIFY(!runtimeInfo.isSymLink());
+        auto expectedPerms = QFile::ReadOwner | QFile::WriteOwner | QFile::ExeOwner
+                | QFile::ReadUser | QFile::WriteUser | QFile::ExeUser;
+        QCOMPARE(QString::number(runtimeInfo.permissions(), 16),
+                 QString::number(expectedPerms, 16));
+    }
 #endif
 }