From 219c54b8a3337456ce5270ded6a67bcde53553d5 Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Mon, 18 Dec 2023 12:26:20 +1000
Subject: [PATCH 3/9] dix: fix DeviceStateNotify event calculation
The previous code only made sense if one considers buttons and keys to
be mutually exclusive on a device. That is not necessarily true, causing
a number of issues.
This function allocates and fills in the number of xEvents we need to
send the device state down the wire. This is split across multiple
32-byte devices including one deviceStateNotify event and optional
deviceKeyStateNotify, deviceButtonStateNotify and (possibly multiple)
deviceValuator events.
The previous behavior would instead compose a sequence
of [state, buttonstate, state, keystate, valuator...]. This is not
protocol correct, and on top of that made the code extremely convoluted.
Fix this by streamlining: add both button and key into the deviceStateNotify
and then append the key state and button state, followed by the
valuators. Finally, the deviceValuator events contain up to 6 valuators
per event but we only ever sent through 3 at a time. Let's double that
troughput.
CVE-2024-0229, ZDI-CAN-22678
This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
---
dix/enterleave.c | 121 ++++++++++++++++++++---------------------------
1 file changed, 52 insertions(+), 69 deletions(-)
diff --git a/dix/enterleave.c b/dix/enterleave.c
index 17964b00a..7b7ba1098 100644
--- a/dix/enterleave.c
+++ b/dix/enterleave.c
@@ -615,9 +615,15 @@ FixDeviceValuator(DeviceIntPtr dev, deviceValuator * ev, ValuatorClassPtr v,
ev->type = DeviceValuator;
ev->deviceid = dev->id;
- ev->num_valuators = nval < 3 ? nval : 3;
+ ev->num_valuators = nval < 6 ? nval : 6;
ev->first_valuator = first;
switch (ev->num_valuators) {
+ case 6:
+ ev->valuator2 = v->axisVal[first + 5];
+ case 5:
+ ev->valuator2 = v->axisVal[first + 4];
+ case 4:
+ ev->valuator2 = v->axisVal[first + 3];
case 3:
ev->valuator2 = v->axisVal[first + 2];
case 2:
@@ -626,7 +632,6 @@ FixDeviceValuator(DeviceIntPtr dev, deviceValuator * ev, ValuatorClassPtr v,
ev->valuator0 = v->axisVal[first];
break;
}
- first += ev->num_valuators;
}
static void
@@ -646,7 +651,7 @@ FixDeviceStateNotify(DeviceIntPtr dev, deviceStateNotify * ev, KeyClassPtr k,
ev->num_buttons = b->numButtons;
memcpy((char *) ev->buttons, (char *) b->down, 4);
}
- else if (k) {
+ if (k) {
ev->classes_reported |= (1 << KeyClass);
ev->num_keys = k->xkbInfo->desc->max_key_code -
k->xkbInfo->desc->min_key_code;
@@ -670,15 +675,26 @@ FixDeviceStateNotify(DeviceIntPtr dev, deviceStateNotify * ev, KeyClassPtr k,
}
}
-
+/**
+ * The device state notify event is split across multiple 32-byte events.
+ * The first one contains the first 32 button state bits, the first 32
+ * key state bits, and the first 3 valuator values.
+ *
+ * If a device has more than that, the server sends out:
+ * - one deviceButtonStateNotify for buttons 32 and above
+ * - one deviceKeyStateNotify for keys 32 and above
+ * - one deviceValuator event per 6 valuators above valuator 4
+ *
+ * All events but the last one have the deviceid binary ORed with MORE_EVENTS,
+ */
static void
DeliverStateNotifyEvent(DeviceIntPtr dev, WindowPtr win)
{
+ /* deviceStateNotify, deviceKeyStateNotify, deviceButtonStateNotify
+ * and one deviceValuator for each 6 valuators */
+ deviceStateNotify sev[3 + (MAX_VALUATORS + 6)/6];
int evcount = 1;
- deviceStateNotify sev[6 + (MAX_VALUATORS + 2)/3];
- deviceStateNotify *ev;
- deviceKeyStateNotify *kev;
- deviceButtonStateNotify *bev;
+ deviceStateNotify *ev = sev;
KeyClassPtr k;
ButtonClassPtr b;
@@ -691,82 +707,49 @@ DeliverStateNotifyEvent(DeviceIntPtr dev, WindowPtr win)
if ((b = dev->button) != NULL) {
nbuttons = b->numButtons;
- if (nbuttons > 32)
+ if (nbuttons > 32) /* first 32 are encoded in deviceStateNotify */
evcount++;
}
if ((k = dev->key) != NULL) {
nkeys = k->xkbInfo->desc->max_key_code - k->xkbInfo->desc->min_key_code;
- if (nkeys > 32)
+ if (nkeys > 32) /* first 32 are encoded in deviceStateNotify */
evcount++;
- if (nbuttons > 0) {
- evcount++;
- }
}
if ((v = dev->valuator) != NULL) {
nval = v->numAxes;
-
- if (nval > 3)
- evcount++;
- if (nval > 6) {
- if (!(k && b))
- evcount++;
- if (nval > 9)
- evcount += ((nval - 7) / 3);
- }
+ /* first three are encoded in deviceStateNotify, then
+ * it's 6 per deviceValuator event */
+ evcount += ((nval - 3) + 6)/6;
}
- ev = sev;
- FixDeviceStateNotify(dev, ev, NULL, NULL, NULL, first);
-
- if (b != NULL) {
- FixDeviceStateNotify(dev, ev++, NULL, b, v, first);
- first += 3;
- nval -= 3;
- if (nbuttons > 32) {
- (ev - 1)->deviceid |= MORE_EVENTS;
- bev = (deviceButtonStateNotify *) ev++;
- bev->type = DeviceButtonStateNotify;
- bev->deviceid = dev->id;
- memcpy((char *) &bev->buttons[4], (char *) &b->down[4],
- DOWN_LENGTH - 4);
- }
- if (nval > 0) {
- (ev - 1)->deviceid |= MORE_EVENTS;
- FixDeviceValuator(dev, (deviceValuator *) ev++, v, first);
- first += 3;
- nval -= 3;
- }
+ BUG_RETURN(evcount <= ARRAY_SIZE(sev));
+
+ FixDeviceStateNotify(dev, ev, k, b, v, first);
+
+ if (b != NULL && nbuttons > 32) {
+ deviceButtonStateNotify *bev = (deviceButtonStateNotify *) ++ev;
+ (ev - 1)->deviceid |= MORE_EVENTS;
+ bev->type = DeviceButtonStateNotify;
+ bev->deviceid = dev->id;
+ memcpy((char *) &bev->buttons[4], (char *) &b->down[4],
+ DOWN_LENGTH - 4);
}
- if (k != NULL) {
- FixDeviceStateNotify(dev, ev++, k, NULL, v, first);
- first += 3;
- nval -= 3;
- if (nkeys > 32) {
- (ev - 1)->deviceid |= MORE_EVENTS;
- kev = (deviceKeyStateNotify *) ev++;
- kev->type = DeviceKeyStateNotify;
- kev->deviceid = dev->id;
- memmove((char *) &kev->keys[0], (char *) &k->down[4], 28);
- }
- if (nval > 0) {
- (ev - 1)->deviceid |= MORE_EVENTS;
- FixDeviceValuator(dev, (deviceValuator *) ev++, v, first);
- first += 3;
- nval -= 3;
- }
+ if (k != NULL && nkeys > 32) {
+ deviceKeyStateNotify *kev = (deviceKeyStateNotify *) ++ev;
+ (ev - 1)->deviceid |= MORE_EVENTS;
+ kev->type = DeviceKeyStateNotify;
+ kev->deviceid = dev->id;
+ memmove((char *) &kev->keys[0], (char *) &k->down[4], 28);
}
+ first = 3;
+ nval -= 3;
while (nval > 0) {
- FixDeviceStateNotify(dev, ev++, NULL, NULL, v, first);
- first += 3;
- nval -= 3;
- if (nval > 0) {
- (ev - 1)->deviceid |= MORE_EVENTS;
- FixDeviceValuator(dev, (deviceValuator *) ev++, v, first);
- first += 3;
- nval -= 3;
- }
+ ev->deviceid |= MORE_EVENTS;
+ FixDeviceValuator(dev, (deviceValuator *) ++ev, v, first);
+ first += 6;
+ nval -= 6;
}
DeliverEventsToWindow(dev, win, (xEvent *) sev, evcount,
--
2.43.0