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100 lines
3.3 KiB
100 lines
3.3 KiB
11 months ago
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From 004f461c440cb6611eefb48fbbb4fa53a6d49f80 Mon Sep 17 00:00:00 2001
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From: Peter Hutterer <peter.hutterer@who-t.net>
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Date: Thu, 5 Oct 2023 12:19:45 +1000
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Subject: [PATCH xserver 2/4] mi: reset the PointerWindows reference on screen
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switch
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PointerWindows[] keeps a reference to the last window our sprite
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entered - changes are usually handled by CheckMotion().
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If we switch between screens via XWarpPointer our
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dev->spriteInfo->sprite->win is set to the new screen's root window.
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If there's another window at the cursor location CheckMotion() will
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trigger the right enter/leave events later. If there is not, it skips
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that process and we never trigger LeaveWindow() - PointerWindows[] for
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the device still refers to the previous window.
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If that window is destroyed we have a dangling reference that will
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eventually cause a use-after-free bug when checking the window hierarchy
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later.
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To trigger this, we require:
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- two protocol screens
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- XWarpPointer to the other screen's root window
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- XDestroyWindow before entering any other window
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This is a niche bug so we hack around it by making sure we reset the
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PointerWindows[] entry so we cannot have a dangling pointer. This
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doesn't handle Enter/Leave events correctly but the previous code didn't
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either.
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CVE-2023-5380, ZDI-CAN-21608
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This vulnerability was discovered by:
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Sri working with Trend Micro Zero Day Initiative
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Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
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Reviewed-by: Adam Jackson <ajax@redhat.com>
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---
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dix/enterleave.h | 2 --
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include/eventstr.h | 3 +++
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mi/mipointer.c | 17 +++++++++++++++--
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3 files changed, 18 insertions(+), 4 deletions(-)
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diff --git a/dix/enterleave.h b/dix/enterleave.h
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index 4b833d8a3b..e8af924c68 100644
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--- a/dix/enterleave.h
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+++ b/dix/enterleave.h
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@@ -58,8 +58,6 @@ extern void DeviceFocusEvent(DeviceIntPtr dev,
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extern void EnterWindow(DeviceIntPtr dev, WindowPtr win, int mode);
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-extern void LeaveWindow(DeviceIntPtr dev);
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-
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extern void CoreFocusEvent(DeviceIntPtr kbd,
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int type, int mode, int detail, WindowPtr pWin);
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diff --git a/include/eventstr.h b/include/eventstr.h
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index bf3b95fe4a..2bae3b0767 100644
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--- a/include/eventstr.h
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+++ b/include/eventstr.h
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@@ -296,4 +296,7 @@ union _InternalEvent {
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#endif
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};
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+extern void
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+LeaveWindow(DeviceIntPtr dev);
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+
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#endif
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diff --git a/mi/mipointer.c b/mi/mipointer.c
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index 75be1aeeb8..b12ae9be1d 100644
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--- a/mi/mipointer.c
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+++ b/mi/mipointer.c
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@@ -397,8 +397,21 @@ miPointerWarpCursor(DeviceIntPtr pDev, ScreenPtr pScreen, int x, int y)
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#ifdef PANORAMIX
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&& noPanoramiXExtension
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#endif
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- )
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- UpdateSpriteForScreen(pDev, pScreen);
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+ ) {
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+ DeviceIntPtr master = GetMaster(pDev, MASTER_POINTER);
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+ /* Hack for CVE-2023-5380: if we're moving
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+ * screens PointerWindows[] keeps referring to the
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+ * old window. If that gets destroyed we have a UAF
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+ * bug later. Only happens when jumping from a window
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+ * to the root window on the other screen.
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+ * Enter/Leave events are incorrect for that case but
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+ * too niche to fix.
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+ */
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+ LeaveWindow(pDev);
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+ if (master)
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+ LeaveWindow(master);
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+ UpdateSpriteForScreen(pDev, pScreen);
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+ }
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}
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/**
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--
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2.41.0
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