Add qt_safe_ftok wrapper for ftok

The ftok function unfortunately can return duplicate keys even for different
files if the same project id is used. This is discussed e.g. in Stevens'
"Advanced Programming in the UNIX Environment".

We want the key to be predictable so we cannot just pass a random number as
the project id. To reduce the propability of key collisions we hash the file
name with the project number as seed for a predictable value. This is the same
approach taken e.g. by Apache, but the real fix is to move away from System V
IPC completely once this is feasible on our supported platforms.

Task-number: QTBUG-48375
Change-Id: If1a57f215f7ddd147aa38919907cfb83db07aea0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/corelib/kernel/qsystemsemaphore_systemv.cpp b/src/corelib/kernel/qsystemsemaphore_systemv.cpp
index 32a4bdef51..490de5f9ee 100644
--- a/src/corelib/kernel/qsystemsemaphore_systemv.cpp
+++ b/src/corelib/kernel/qsystemsemaphore_systemv.cpp
@@ -85,7 +85,7 @@ key_t QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
     createdFile = (1 == built);
 
     // Get the unix key for the created file
-    unix_key = ftok(QFile::encodeName(fileName).constData(), 'Q');
+    unix_key = qt_safe_ftok(QFile::encodeName(fileName), 'Q');
     if (-1 == unix_key) {
         errorString = QCoreApplication::tr("%1: ftok failed", "QSystemSemaphore").arg(QLatin1String("QSystemSemaphore::handle:"));
         error = QSystemSemaphore::KeyError;