From b2c0a783d0d554b39d21b4daaf9143311b9f96f3 Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Thu, 17 Nov 2022 15:25:37 +0200
Subject: [PATCH] Client: Add F_SEAL_SHRINK seal to shm backing file

This lets libwayland-server avoid installing a SIGBUS handler when it
wants to mmap() the backing file and access the contents of shared
memory client buffers.

Change-Id: Id0b17f729799535d73e8700c5a99c32fd88a068a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: David Edmundson <davidedmundson@kde.org>
---
 src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
index a8e59637a1f..2e0c2491fe4 100644
--- a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
+++ b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
@@ -16,6 +16,7 @@
 
 #include <QtWaylandClient/private/wayland-wayland-client-protocol.h>
 
+#include <fcntl.h>
 #include <unistd.h>
 #include <sys/mman.h>
 
@@ -25,6 +26,9 @@
 #  ifndef MFD_CLOEXEC
 #    define MFD_CLOEXEC     0x0001U
 #  endif
+#  ifndef MFD_ALLOW_SEALING
+#    define MFD_ALLOW_SEALING 0x0002U
+#  endif
 #endif
 
 QT_BEGIN_NAMESPACE
@@ -39,7 +43,9 @@ QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
     int fd = -1;
 
 #ifdef SYS_memfd_create
-    fd = syscall(SYS_memfd_create, "wayland-shm", MFD_CLOEXEC);
+    fd = syscall(SYS_memfd_create, "wayland-shm", MFD_CLOEXEC | MFD_ALLOW_SEALING);
+    if (fd >= 0)
+        fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_SEAL);
 #endif
 
     QScopedPointer<QFile> filePointer;