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From 947bd1b3f4a23565bf10879ec41ba06ebe1e1c76 Mon Sep 17 00:00:00 2001
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From: Olivier Fourdan <ofourdan@redhat.com>
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Date: Mon, 13 Mar 2023 11:08:47 +0100
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Subject: [PATCH xserver] composite: Fix use-after-free of the COW
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ZDI-CAN-19866/CVE-2023-1393
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If a client explicitly destroys the compositor overlay window (aka COW),
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we would leave a dangling pointer to that window in the CompScreen
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structure, which will trigger a use-after-free later.
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Make sure to clear the CompScreen pointer to the COW when the latter gets
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destroyed explicitly by the client.
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This vulnerability was discovered by:
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Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
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Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
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Reviewed-by: Adam Jackson <ajax@redhat.com>
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---
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composite/compwindow.c | 5 +++++
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1 file changed, 5 insertions(+)
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diff --git a/composite/compwindow.c b/composite/compwindow.c
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index 4e2494b86..b30da589e 100644
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--- a/composite/compwindow.c
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+++ b/composite/compwindow.c
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@@ -620,6 +620,11 @@ compDestroyWindow(WindowPtr pWin)
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ret = (*pScreen->DestroyWindow) (pWin);
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cs->DestroyWindow = pScreen->DestroyWindow;
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pScreen->DestroyWindow = compDestroyWindow;
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+
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+ /* Did we just destroy the overlay window? */
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+ if (pWin == cs->pOverlayWin)
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+ cs->pOverlayWin = NULL;
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+
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/* compCheckTree (pWin->drawable.pScreen); can't check -- tree isn't good*/
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return ret;
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}
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--
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2.40.0
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