From 26769aa71fcbe0a8403b7fb13b7c9010cc07c3a8 Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Fri, 5 Jan 2024 09:40:27 +1000
Subject: [PATCH] dix: when disabling a master, float disabled slaved devices
 too

Disabling a master device floats all slave devices but we didn't do this
to already-disabled slave devices. As a result those devices kept their
reference to the master device resulting in access to already freed
memory if the master device was removed before the corresponding slave
device.

And to match this behavior, also forcibly reset that pointer during
CloseDownDevices().

Related to CVE-2024-21886, ZDI-CAN-22840
---
 dix/devices.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/dix/devices.c b/dix/devices.c
index 389d28a23c..84a6406d13 100644
--- a/dix/devices.c
+++ b/dix/devices.c
@@ -483,6 +483,13 @@ DisableDevice(DeviceIntPtr dev, BOOL sendevent)
                 flags[other->id] |= XISlaveDetached;
             }
         }
+
+        for (other = inputInfo.off_devices; other; other = other->next) {
+            if (!IsMaster(other) && GetMaster(other, MASTER_ATTACHED) == dev) {
+                AttachDevice(NULL, other, NULL);
+                flags[other->id] |= XISlaveDetached;
+            }
+        }
     }
     else {
         for (other = inputInfo.devices; other; other = other->next) {
@@ -1088,6 +1095,11 @@ CloseDownDevices(void)
             dev->master = NULL;
     }
 
+    for (dev = inputInfo.off_devices; dev; dev = dev->next) {
+        if (!IsMaster(dev) && !IsFloating(dev))
+            dev->master = NULL;
+    }
+
     CloseDeviceList(&inputInfo.devices);
     CloseDeviceList(&inputInfo.off_devices);
 
-- 
GitLab

