Fix crashes when accessing environment variables concurrently

We've seen crashes with QThreadPrivate::start using qgetenv during the creation
of the event dispatcher, while another thread (for example the gui thread)
called qputenv. This is inherently thread-unsafe and there are many places
where we make the assumption that using the environment is safe. However access
to the environment is inherently unsafe in the C runtime and the best that we
can do is add a mutex around the Qt environment access functions, to at least
protect ourselves and our users.

Change-Id: Ie9a718d9f7ce63c423c645f0be3e3f4933e1cb08
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

2 files changed, 5 insertions, 5 deletions

diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index ed0193c256..5ea3bf8982 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -405,7 +405,7 @@ void QProcessPrivate::startProcess()
     char **path = 0;
     int pathc = 0;
     if (!program.contains(QLatin1Char('/'))) {
-        const QString pathEnv = QString::fromLocal8Bit(::getenv("PATH"));
+        const QString pathEnv = QString::fromLocal8Bit(qgetenv("PATH"));
         if (!pathEnv.isEmpty()) {
             QStringList pathEntries = pathEnv.split(QLatin1Char(':'), QString::SkipEmptyParts);
             if (!pathEntries.isEmpty()) {
@@ -1187,7 +1187,7 @@ bool QProcessPrivate::startDetached(const QString &program, const QStringList &a
             argv[arguments.size() + 1] = 0;
 
             if (!program.contains(QLatin1Char('/'))) {
-                const QString path = QString::fromLocal8Bit(::getenv("PATH"));
+                const QString path = QString::fromLocal8Bit(qgetenv("PATH"));
                 if (!path.isEmpty()) {
                     QStringList pathEntries = path.split(QLatin1Char(':'));
                     for (int k = 0; k < pathEntries.size(); ++k) {
diff --git a/src/corelib/io/qsettings.cpp b/src/corelib/io/qsettings.cpp
index afe68125d4..cb6de29532 100644
--- a/src/corelib/io/qsettings.cpp
+++ b/src/corelib/io/qsettings.cpp
@@ -1048,12 +1048,12 @@ static void initDefaultPaths(QMutexLocker *locker)
         // Non XDG platforms (OS X, iOS, Blackberry, Android...) have used this code path erroneously
         // for some time now. Moving away from that would require migrating existing settings.
         QString userPath;
-        char *env = getenv("XDG_CONFIG_HOME");
-        if (env == 0) {
+        QByteArray env = qgetenv("XDG_CONFIG_HOME");
+        if (env.isEmpty()) {
             userPath = QDir::homePath();
             userPath += QLatin1Char('/');
             userPath += QLatin1String(".config");
-        } else if (*env == '/') {
+        } else if (env.startsWith('/')) {
             userPath = QFile::decodeName(env);
         } else {
             userPath = QDir::homePath();