xserver: Branch 'master'

[GitLab Mirror]

 composite/compwindow.c |    5 +++++
 1 file changed, 5 insertions(+)

New commits:
commit 26ef545b3502f61ca722a7a3373507e88ef64110
Author: Olivier Fourdan <ofourdan at redhat.com>
Date:   Mon Mar 13 11:08:47 2023 +0100

    composite: Fix use-after-free of the COW
    
    ZDI-CAN-19866/CVE-2023-1393
    
    If a client explicitly destroys the compositor overlay window (aka COW),
    we would leave a dangling pointer to that window in the CompScreen
    structure, which will trigger a use-after-free later.
    
    Make sure to clear the CompScreen pointer to the COW when the latter gets
    destroyed explicitly by the client.
    
    This vulnerability was discovered by:
    Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
    
    Signed-off-by: Olivier Fourdan <ofourdan at redhat.com>
    Reviewed-by: Adam Jackson <ajax at redhat.com>

diff --git a/composite/compwindow.c b/composite/compwindow.c
index 4e2494b86..b30da589e 100644
--- a/composite/compwindow.c
+++ b/composite/compwindow.c
@@ -620,6 +620,11 @@ compDestroyWindow(WindowPtr pWin)
     ret = (*pScreen->DestroyWindow) (pWin);
     cs->DestroyWindow = pScreen->DestroyWindow;
     pScreen->DestroyWindow = compDestroyWindow;
+
+    /* Did we just destroy the overlay window? */
+    if (pWin == cs->pOverlayWin)
+        cs->pOverlayWin = NULL;
+
 /*    compCheckTree (pWin->drawable.pScreen); can't check -- tree isn't good*/
     return ret;
 }