72 lines
2.9 KiB
Diff
72 lines
2.9 KiB
Diff
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From 215f894965df5fb0bb45b107d84524e700d2073c Mon Sep 17 00:00:00 2001
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From: Michal Srb <msrb@suse.com>
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Date: Wed, 24 May 2017 15:54:40 +0300
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Subject: [PATCH] dix: Disallow GenericEvent in SendEvent request.
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The SendEvent request holds xEvent which is exactly 32 bytes long, no more,
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no less. Both ProcSendEvent and SProcSendEvent verify that the received data
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exactly match the request size. However nothing stops the client from passing
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in event with xEvent::type = GenericEvent and any value of
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xGenericEvent::length.
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In the case of ProcSendEvent, the event will be eventually passed to
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WriteEventsToClient which will see that it is Generic event and copy the
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arbitrary length from the receive buffer (and possibly past it) and send it to
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the other client. This allows clients to copy unitialized heap memory out of X
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server or to crash it.
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In case of SProcSendEvent, it will attempt to swap the incoming event by
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calling a swapping function from the EventSwapVector array. The swapped event
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is written to target buffer, which in this case is local xEvent variable. The
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xEvent variable is 32 bytes long, but the swapping functions for GenericEvents
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expect that the target buffer has size matching the size of the source
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GenericEvent. This allows clients to cause stack buffer overflows.
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Signed-off-by: Michal Srb <msrb@suse.com>
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Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
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Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
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Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
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---
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dix/events.c | 6 ++++++
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dix/swapreq.c | 7 +++++++
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2 files changed, 13 insertions(+)
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diff --git a/dix/events.c b/dix/events.c
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index 3e3a01ef9..d3a33ea3f 100644
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--- a/dix/events.c
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+++ b/dix/events.c
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@@ -5366,6 +5366,12 @@ ProcSendEvent(ClientPtr client)
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client->errorValue = stuff->event.u.u.type;
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return BadValue;
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}
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+ /* Generic events can have variable size, but SendEvent request holds
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+ exactly 32B of event data. */
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+ if (stuff->event.u.u.type == GenericEvent) {
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+ client->errorValue = stuff->event.u.u.type;
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+ return BadValue;
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+ }
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if (stuff->event.u.u.type == ClientMessage &&
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stuff->event.u.u.detail != 8 &&
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stuff->event.u.u.detail != 16 && stuff->event.u.u.detail != 32) {
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diff --git a/dix/swapreq.c b/dix/swapreq.c
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index 719e9b81c..67850593b 100644
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--- a/dix/swapreq.c
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+++ b/dix/swapreq.c
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@@ -292,6 +292,13 @@ SProcSendEvent(ClientPtr client)
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swapl(&stuff->destination);
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swapl(&stuff->eventMask);
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+ /* Generic events can have variable size, but SendEvent request holds
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+ exactly 32B of event data. */
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+ if (stuff->event.u.u.type == GenericEvent) {
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+ client->errorValue = stuff->event.u.u.type;
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+ return BadValue;
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+ }
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+
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/* Swap event */
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proc = EventSwapVector[stuff->event.u.u.type & 0177];
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if (!proc || proc == NotImplemented) /* no swapping proc; invalid event type? */
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--
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2.11.0
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