From 0c1a93d319558fe3ab2d94f51d174b4f93810afd Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Tue, 28 Nov 2023 15:19:04 +1000
Subject: [PATCH] Xi: allocate enough XkbActions for our buttons

button->xkb_acts is supposed to be an array sufficiently large for all
our buttons, not just a single XkbActions struct. Allocating
insufficient memory here means when we memcpy() later in
XkbSetDeviceInfo we write into memory that wasn't ours to begin with,
leading to the usual security ooopsiedaisies.

CVE-2023-6377, ZDI-CAN-22412, ZDI-CAN-22413

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
---
 Xi/exevents.c | 12 ++++++------
 dix/devices.c | 10 ++++++++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/Xi/exevents.c b/Xi/exevents.c
index dcd4efb3bc..54ea11a938 100644
--- a/Xi/exevents.c
+++ b/Xi/exevents.c
@@ -611,13 +611,13 @@ DeepCopyPointerClasses(DeviceIntPtr from, DeviceIntPtr to)
         }

         if (from->button->xkb_acts) {
-            if (!to->button->xkb_acts) {
-                to->button->xkb_acts = calloc(1, sizeof(XkbAction));
-                if (!to->button->xkb_acts)
-                    FatalError("[Xi] not enough memory for xkb_acts.\n");
-            }
+            size_t maxbuttons = max(to->button->numButtons, from->button->numButtons);
+            to->button->xkb_acts = xnfreallocarray(to->button->xkb_acts,
+                                                   maxbuttons,
+                                                   sizeof(XkbAction));
+            memset(to->button->xkb_acts, 0, maxbuttons * sizeof(XkbAction));
             memcpy(to->button->xkb_acts, from->button->xkb_acts,
-                   sizeof(XkbAction));
+                   from->button->numButtons * sizeof(XkbAction));
         }
         else {
             free(to->button->xkb_acts);
diff --git a/dix/devices.c b/dix/devices.c
index b063128df0..3f3224d626 100644
--- a/dix/devices.c
+++ b/dix/devices.c
@@ -2539,6 +2539,8 @@ RecalculateMasterButtons(DeviceIntPtr slave)

     if (master->button && master->button->numButtons != maxbuttons) {
         int i;
+        int last_num_buttons = master->button->numButtons;
+
         DeviceChangedEvent event = {
             .header = ET_Internal,
             .type = ET_DeviceChanged,
@@ -2549,6 +2551,14 @@ RecalculateMasterButtons(DeviceIntPtr slave)
         };

         master->button->numButtons = maxbuttons;
+        if (last_num_buttons < maxbuttons) {
+            master->button->xkb_acts = xnfreallocarray(master->button->xkb_acts,
+                                                       maxbuttons,
+                                                       sizeof(XkbAction));
+            memset(&master->button->xkb_acts[last_num_buttons],
+                   0,
+                   (maxbuttons - last_num_buttons) * sizeof(XkbAction));
+        }

         memcpy(&event.buttons.names, master->button->labels, maxbuttons *
                sizeof(Atom));
--
GitLab