Fix CVE-2016-7951 and CVE-2016-7952
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-7951
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-7952
Patch copied from upstream source repository:
https://cgit.freedesktop.org/xorg/lib/libXtst/commit/?id=9556ad67af3129ec4a7a4f4b54a0d59701beeae3
From 9556ad67af3129ec4a7a4f4b54a0d59701beeae3 Mon Sep 17 00:00:00 2001
From: Tobias Stoeckmann <tobias@stoeckmann.org>
Date: Sun, 25 Sep 2016 21:37:01 +0200
Subject: [PATCH] Out of boundary access and endless loop in libXtst
A lack of range checks in libXtst allows out of boundary accesses.
The checks have to be done in-place here, because it cannot be done
without in-depth knowledge of the read data.
If XRecordStartOfData, XRecordEndOfData, or XRecordClientDied
without a client sequence have attached data, an endless loop would
occur. The do-while-loop continues until the current index reaches
the end. But in these cases, the current index would not be
incremented, leading to an endless processing.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>
---
src/XRecord.c | 43 +++++++++++++++++++++++++++++++++++++++----
1 file changed, 39 insertions(+), 4 deletions(-)
diff --git a/src/XRecord.c b/src/XRecord.c
index 50420c0..fefd842 100644
--- a/src/XRecord.c
+++ b/src/XRecord.c
@@ -749,15 +749,23 @@ parse_reply_call_callback(
switch (rep->category) {
case XRecordFromServer:
if (rep->elementHeader&XRecordFromServerTime) {
+ if (current_index + 4 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index,
data->server_time);
current_index += 4;
}
+ if (current_index + 1 > rep->length << 2)
+ return Error;
switch (reply->buf[current_index]) {
case X_Reply: /* reply */
+ if (current_index + 8 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index+4, datum_bytes);
+ if (datum_bytes < 0 || datum_bytes > ((INT_MAX >> 2) - 8))
+ return Error;
datum_bytes = (datum_bytes+8) << 2;
break;
default: /* error or event */
@@ -766,52 +774,73 @@ parse_reply_call_callback(
break;
case XRecordFromClient:
if (rep->elementHeader&XRecordFromClientTime) {
+ if (current_index + 4 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index,
data->server_time);
current_index += 4;
}
if (rep->elementHeader&XRecordFromClientSequence) {
+ if (current_index + 4 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index,
data->client_seq);
current_index += 4;
}
+ if (current_index + 4 > rep->length<<2)
+ return Error;
if (reply->buf[current_index+2] == 0
&& reply->buf[current_index+3] == 0) /* needn't swap 0 */
{ /* BIG-REQUESTS */
+ if (current_index + 8 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index+4, datum_bytes);
} else {
EXTRACT_CARD16(rep->clientSwapped,
reply->buf+current_index+2, datum_bytes);
}
+ if (datum_bytes < 0 || datum_bytes > INT_MAX >> 2)
+ return Error;
datum_bytes <<= 2;
break;
case XRecordClientStarted:
+ if (current_index + 8 > rep->length << 2)
+ return Error;
EXTRACT_CARD16(rep->clientSwapped,
reply->buf+current_index+6, datum_bytes);
datum_bytes = (datum_bytes+2) << 2;
break;
case XRecordClientDied:
if (rep->elementHeader&XRecordFromClientSequence) {
+ if (current_index + 4 > rep->length << 2)
+ return Error;
EXTRACT_CARD32(rep->clientSwapped,
reply->buf+current_index,
data->client_seq);
current_index += 4;
- }
- /* fall through */
+ } else if (current_index < rep->length << 2)
+ return Error;
+ datum_bytes = 0;
+ break;
case XRecordStartOfData:
case XRecordEndOfData:
+ if (current_index < rep->length << 2)
+ return Error;
datum_bytes = 0;
+ break;
}
if (datum_bytes > 0) {
- if (current_index + datum_bytes > rep->length << 2)
+ if (INT_MAX - datum_bytes < (rep->length << 2) - current_index) {
fprintf(stderr,
"XRecord: %lu-byte reply claims %d-byte element (seq %lu)\n",
- (long)rep->length << 2, current_index + datum_bytes,
+ (unsigned long)rep->length << 2, current_index + datum_bytes,
dpy->last_request_read);
+ return Error;
+ }
/*
* This assignment (and indeed the whole buffer sharing
* scheme) assumes arbitrary 4-byte boundaries are
@@ -863,6 +892,12 @@ XRecordEnableContext(Display *dpy, XRecordContext context,
return 0;
}
+ if (rep.length > INT_MAX >> 2) {
+ UnlockDisplay(dpy);
+ SyncHandle();
+ return 0;
+ }
+
if (rep.length > 0) {
reply = alloc_reply_buffer(info, rep.length<<2);
if (!reply) {
--
2.10.1