Make QTemporaryDir file name more random

qrand() returns a number between 0 and RAND_MAX, which is only
guaranteed to be bigger than 32767. Dividing it repeatedly means
that the last bytes are always 0.

[ChangeLog][QtCore][QTemporaryDir] Fixed bug in QTemporaryDir name generator that dramatically
reduced randomness of the name.

Change-Id: I90613a652e6384296aed827e2714fe63cd8797ee
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>

1 files changed, 25 insertions, 14 deletions

diff --git a/src/corelib/io/qtemporarydir.cpp b/src/corelib/io/qtemporarydir.cpp
index 483a76fa82..2c526847b4 100644
--- a/src/corelib/io/qtemporarydir.cpp
+++ b/src/corelib/io/qtemporarydir.cpp
@@ -94,9 +94,19 @@ static QString defaultTemplateName()
     return QDir::tempPath() + QLatin1Char('/') + baseName + QLatin1String("-XXXXXX");
 }
 
+#if defined(Q_OS_QNX ) || defined(Q_OS_WIN) || defined(Q_OS_ANDROID)
+
+static int nextRand(int &v)
+{
+    int r = v % 62;
+    v /= 62;
+    if (v < 62)
+        v = qrand();
+    return r;
+}
+
 static char *q_mkdtemp(char *templateName)
 {
-#if defined(Q_OS_QNX ) || defined(Q_OS_WIN) || defined(Q_OS_ANDROID)
     static const char letters[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
     const size_t length = strlen(templateName);
@@ -110,16 +120,11 @@ static char *q_mkdtemp(char *templateName)
         int v = qrand();
 
         /* Fill in the random bits.  */
-        XXXXXX[0] = letters[v % 62];
-        v /= 62;
-        XXXXXX[1] = letters[v % 62];
-        v /= 62;
-        XXXXXX[2] = letters[v % 62];
-        v /= 62;
-        XXXXXX[3] = letters[v % 62];
-        v /= 62;
-        XXXXXX[4] = letters[v % 62];
-        v /= 62;
+        XXXXXX[0] = letters[nextRand(v)];
+        XXXXXX[1] = letters[nextRand(v)];
+        XXXXXX[2] = letters[nextRand(v)];
+        XXXXXX[3] = letters[nextRand(v)];
+        XXXXXX[4] = letters[nextRand(v)];
         XXXXXX[5] = letters[v % 62];
 
         QString templateNameStr = QFile::decodeName(templateName);
@@ -137,11 +142,17 @@ static char *q_mkdtemp(char *templateName)
         }
     }
     return 0;
-#else
-    return mkdtemp(templateName);
-#endif
 }
 
+#else // defined(Q_OS_QNX ) || defined(Q_OS_WIN) || defined(Q_OS_ANDROID)
+
+static char *q_mkdtemp(char *templateName)
+{
+   return mkdtemp(templateName);
+}
+
+#endif
+
 void QTemporaryDirPrivate::create(const QString &templateName)
 {
     QByteArray buffer = QFile::encodeName(templateName);