xcb: Fix access to shm for X server running from another user

Use ShmCreateSegment call, that was added in MIT-SHM 1.2, to
create shared memory segments on the server side. It returns
a POSIX shared memory object that is used to mmap memory.
It's in effect a file descriptor that is passed through the
X server socket and thus avoids permission checks.
On the other hand this scheme is more secure, because the
file descriptor, and thus the shared memory, are accessible
only by the X server and the application.

Task-number: QTBUG-46017
Change-Id: I202eead9d01aee2ab5b65f4f74f4c13da7cb2239
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index b2713b8ac7..dbc1c4561d 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -480,6 +480,7 @@ public:
     bool hasXRender() const { return has_render_extension; }
     bool hasXInput2() const { return m_xi2Enabled; }
     bool hasShm() const { return has_shm; }
+    bool hasShmFd() const { return has_shm_fd; }
 
     bool threadedEventHandling() const { return m_reader->isRunning(); }
 
@@ -703,6 +704,7 @@ private:
     bool has_xkb = false;
     bool has_render_extension = false;
     bool has_shm = false;
+    bool has_shm_fd = false;
 
     Qt::MouseButtons m_buttonState = 0;
     Qt::MouseButton m_button = Qt::NoButton;