From 936d34bdff4c479ccd0405fc221ff8e4c6c7014d Mon Sep 17 00:00:00 2001 From: Peter Hutterer Date: Tue, 29 Nov 2022 12:55:45 +1000 Subject: [PATCH] Xtest: disallow GenericEvents in XTestSwapFakeInput XTestSwapFakeInput assumes all events in this request are sizeof(xEvent) and iterates through these in 32-byte increments. However, a GenericEvent may be of arbitrary length longer than 32 bytes, so any GenericEvent in this list would result in subsequent events to be misparsed. Additional, the swapped event is written into a stack-allocated struct xEvent (size 32 bytes). For any GenericEvent longer than 32 bytes, swapping the event may thus smash the stack like an avocado on toast. Catch this case early and return BadValue for any GenericEvent. Which is what would happen in unswapped setups anyway since XTest doesn't support GenericEvent. CVE-2022-46340, ZDI-CAN 19265 This vulnerability was discovered by: Jan-Niklas Sohn working with Trend Micro Zero Day Initiative Signed-off-by: Peter Hutterer Acked-by: Olivier Fourdan (cherry picked from commit b320ca0ffe4c0c872eeb3a93d9bde21f765c7c63) --- Xext/xtest.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/Xext/xtest.c b/Xext/xtest.c index 540d270a1..e5d38aa61 100644 --- a/Xext/xtest.c +++ b/Xext/xtest.c @@ -502,10 +502,11 @@ XTestSwapFakeInput(ClientPtr client, xReq * req) nev = ((req->length << 2) - sizeof(xReq)) / sizeof(xEvent); for (ev = (xEvent *) &req[1]; --nev >= 0; ev++) { + int evtype = ev->u.u.type & 0x177; /* Swap event */ - proc = EventSwapVector[ev->u.u.type & 0177]; + proc = EventSwapVector[evtype]; /* no swapping proc; invalid event type? */ - if (!proc || proc == NotImplemented) { + if (!proc || proc == NotImplemented || evtype == GenericEvent) { client->errorValue = ev->u.u.type; return BadValue; }