From 06eb55528bb62f7418f740152642f2066d593bbf Mon Sep 17 00:00:00 2001 From: Peter Hutterer Date: Tue, 29 Nov 2022 14:53:07 +1000 Subject: [PATCH xserver 5/6] Xext: free the screen saver resource when replacing it This fixes a use-after-free bug: When a client first calls ScreenSaverSetAttributes(), a struct ScreenSaverAttrRec is allocated and added to the client's resources. When the same client calls ScreenSaverSetAttributes() again, a new struct ScreenSaverAttrRec is allocated, replacing the old struct. The old struct was freed but not removed from the clients resources. Later, when the client is destroyed the resource system invokes ScreenSaverFreeAttr and attempts to clean up the already freed struct. Fix this by letting the resource system free the old attrs instead. ZDI-CAN 19404 This vulnerability was discovered by: Jan-Niklas Sohn working with Trend Micro Zero Day Initiative Signed-off-by: Peter Hutterer --- Xext/saver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Xext/saver.c b/Xext/saver.c index f813ba08d1..fd6153c313 100644 --- a/Xext/saver.c +++ b/Xext/saver.c @@ -1051,7 +1051,7 @@ ScreenSaverSetAttributes(ClientPtr client) pVlist++; } if (pPriv->attr) - FreeScreenAttr(pPriv->attr); + FreeResource(pPriv->attr->resource, AttrType); pPriv->attr = pAttr; pAttr->resource = FakeClientID(client->index); if (!AddResource(pAttr->resource, AttrType, (void *) pAttr)) -- 2.38.1