path: root/dix/events.c
diff options
authorMichal Srb <>2017-05-24 15:54:40 +0300
committerPeter Hutterer <>2017-06-19 11:58:50 +1000
commit215f894965df5fb0bb45b107d84524e700d2073c (patch)
treeebe3a7eb03580d8e52649a5bc8e7ee017733af06 /dix/events.c
parent05442de962d3dc624f79fc1a00eca3ffc5489ced (diff)
dix: Disallow GenericEvent in SendEvent request.
The SendEvent request holds xEvent which is exactly 32 bytes long, no more, no less. Both ProcSendEvent and SProcSendEvent verify that the received data exactly match the request size. However nothing stops the client from passing in event with xEvent::type = GenericEvent and any value of xGenericEvent::length. In the case of ProcSendEvent, the event will be eventually passed to WriteEventsToClient which will see that it is Generic event and copy the arbitrary length from the receive buffer (and possibly past it) and send it to the other client. This allows clients to copy unitialized heap memory out of X server or to crash it. In case of SProcSendEvent, it will attempt to swap the incoming event by calling a swapping function from the EventSwapVector array. The swapped event is written to target buffer, which in this case is local xEvent variable. The xEvent variable is 32 bytes long, but the swapping functions for GenericEvents expect that the target buffer has size matching the size of the source GenericEvent. This allows clients to cause stack buffer overflows. Signed-off-by: Michal Srb <> Reviewed-by: Peter Hutterer <> Signed-off-by: Peter Hutterer <>
Diffstat (limited to 'dix/events.c')
1 files changed, 6 insertions, 0 deletions
diff --git a/dix/events.c b/dix/events.c
index 3e3a01ef9..d3a33ea3f 100644
--- a/dix/events.c
+++ b/dix/events.c
@@ -5366,6 +5366,12 @@ ProcSendEvent(ClientPtr client)
client->errorValue = stuff->event.u.u.type;
return BadValue;
+ /* Generic events can have variable size, but SendEvent request holds
+ exactly 32B of event data. */
+ if (stuff->event.u.u.type == GenericEvent) {
+ client->errorValue = stuff->event.u.u.type;
+ return BadValue;
+ }
if (stuff->event.u.u.type == ClientMessage &&
stuff->event.u.u.detail != 8 &&
stuff->event.u.u.detail != 16 && stuff->event.u.u.detail != 32) {