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Out of boundary access and endless loop in libXtst

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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.

From Tobias Stoeckmann / X.Org security advisory Oct 4, 2016
This commit is contained in:
matthieu 2016-10-04 15:08:08 +00:00
parent 26cabdb32f
commit ce0f69616f
1 changed files with 39 additions and 4 deletions
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43
lib/libXtst/src/XRecord.c
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@ -760,15 +760,23 @@ 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 */
@ -777,52 +785,73 @@ 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
@ -874,6 +903,12 @@ 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) {