Fix leaking of FDs requested from logind

Summary:
The takeDevice method calls dup, but that syscall removes the O_CLOEXEC flag
as a side-effect. This resulted in all child processes of kwin_wayland having
an open file descriptor for those devices.

Test Plan:
Looked at the open FDs of the startplasma script. Before, all
/dev/input/eventX files and /dev/dri/card0 were open. Now, none of those
are part of /proc/PID/fd/

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: kwin, plasma-devel, #kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D8887

logind.cpp

@@ -36,6 +36,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef major
 #include <sys/types.h>
 #endif
+#include <fcntl.h>
 #include <unistd.h>
 #include "utils.h"
 
@@ -378,7 +379,9 @@ int LogindIntegration::takeDevice(const char *path)
         qCDebug(KWIN_CORE) << "Could not take device" << path << ", cause: " << reply.errorMessage();
         return -1;
     }
-    return dup(reply.arguments().first().value<QDBusUnixFileDescriptor>().fileDescriptor());
+
+    // The dup syscall removes the CLOEXEC flag as a side-effect. So use fcntl's F_DUPFD_CLOEXEC cmd.
+    return fcntl(reply.arguments().first().value<QDBusUnixFileDescriptor>().fileDescriptor(), F_DUPFD_CLOEXEC, 0);
 }
 
 void LogindIntegration::releaseDevice(int fd)