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hw/xfree86: Avoid cursor use after free 

During a VT-Switch a raw pointer to the shared cursor object
is saved which is then freed (in case of low refcount) by a call to
xf86CursorSetCursor with argument pCurs = NullCursor.
This leads to a dangling pointer which can follow in a use after free.

This fix ensures that there is a shared handle saved for the VT-Switch cycle.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
(cherry picked from commit 7ae221ad57)
This commit is contained in:
Martin Weber 2020-07-21 18:24:41 +02:00 committed by Matt Turner
parent 0679d46605
commit c726ceacc1
1 changed files with 2 additions and 1 deletions
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3
hw/xfree86/ramdac/xf86CursorRD.c
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@ -212,7 +212,7 @@ xf86CursorEnableDisableFBAccess(ScrnInfoPtr pScrn, Bool enable)
xf86CursorScreenKey); xf86CursorScreenKey);
if (!enable && ScreenPriv->CurrentCursor != NullCursor) { if (!enable && ScreenPriv->CurrentCursor != NullCursor) {
CursorPtr currentCursor = ScreenPriv->CurrentCursor; CursorPtr currentCursor = RefCursor(ScreenPriv->CurrentCursor);
xf86CursorSetCursor(pDev, pScreen, NullCursor, ScreenPriv->x, xf86CursorSetCursor(pDev, pScreen, NullCursor, ScreenPriv->x,
ScreenPriv->y); ScreenPriv->y);
@ -231,6 +231,7 @@ xf86CursorEnableDisableFBAccess(ScrnInfoPtr pScrn, Bool enable)
*/ */
xf86CursorSetCursor(pDev, pScreen, ScreenPriv->SavedCursor, xf86CursorSetCursor(pDev, pScreen, ScreenPriv->SavedCursor,
ScreenPriv->x, ScreenPriv->y); ScreenPriv->x, ScreenPriv->y);
UnrefCursor(ScreenPriv->SavedCursor);
ScreenPriv->SavedCursor = NULL; ScreenPriv->SavedCursor = NULL;
} }
} }