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bounds-check dns response parsing against packet end #1628

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bounds-check dns response parsing against packet end #1628

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75 changes: 53 additions & 22 deletions modules/network/dns/moddnsparser.c
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2018-2022 Moddable Tech, Inc.
* Copyright (c) 2018-2026 Moddable Tech, Inc.
*
* This file is part of the Moddable SDK Runtime.
*
Expand Down Expand Up @@ -33,6 +33,8 @@ static void *getPacket(xsMachine *the, uint8_t **end)
xsmcGetBufferReadable(xsResult, (void **)&result, &length);
if (end)
*end = length + (uint8_t *)result;
if (length < 12)
xsUnknownError("invalid packet header");
return result;
}

Expand All @@ -50,7 +52,7 @@ static void *getQuestionByIndex(xsMachine *the, uint8_t index)

position += 12;
while (index--) {
while (true) {
while (position < packetEnd) {
uint8_t tag = *position++;
if (0 == tag)
break;
Expand All @@ -74,6 +76,8 @@ static void *getAnswerByIndex(xsMachine *the, uint8_t index)
uint8_t *position = getPacket(the, &packetEnd);
uint16_t answers = ((position[6] << 8) | position[7]) + ((position[8] << 8) | position[9]) + ((position[10] << 8) | position[11]); // including authority and additional records
position = getQuestionByIndex(the, 0xff);
if (!position)
return NULL;

if ((0xff != index) && (index >= answers))
return NULL;
Expand All @@ -84,23 +88,27 @@ static void *getAnswerByIndex(xsMachine *the, uint8_t index)
while (index--) {
uint16_t rdlength;

while (true) {
while (position < packetEnd) {
uint8_t tag = *position++;
if (0 == tag)
break;
if (0xC0 == (tag & 0xC0)) {
position += 1;
break;
}
if ((packetEnd - position) < tag)
return NULL;
position += tag;
}
if ((packetEnd - position) < 10)
return NULL;
position += 10;
if (position >= packetEnd)
if (position > packetEnd)
return NULL;

rdlength = (position[-2] << 8) | position[-1];
position += rdlength;
if (position >= packetEnd)
if (position > packetEnd)
return NULL;
}

Expand All @@ -109,38 +117,46 @@ static void *getAnswerByIndex(xsMachine *the, uint8_t index)

static int parseQname(xsMachine *the, int offset)
{
uint8_t *position;
uint8_t *packet, *position, *packetEnd;
int qnameEndPosition = 0;

xsVar(1) = xsNewArray(0);
position = offset + (uint8_t *)getPacket(the, NULL);;
while (true) {
packet = (uint8_t *)getPacket(the, &packetEnd);
position = packet + offset;
while (position < packetEnd) {
char tmp[64];
uint8_t tag = *position++;
offset += 1;
if (0 == tag) {
if (0 == qnameEndPosition)
qnameEndPosition = offset;
break;
return qnameEndPosition;
}
if (0xC0 == (tag & 0xC0)) {
if (position >= packetEnd)
break;
if (0 == qnameEndPosition)
qnameEndPosition = offset + 1;
offset = ((tag << 8) | *position) & 0x3FFF; //@@ range check
position = offset + (uint8_t *)getPacket(the, NULL);
offset = ((tag << 8) | *position) & 0x3FFF;
if ((uint32_t)offset > (uint32_t)(packetEnd - packet))
break;
position = packet + offset;
continue;
}

if (tag > 63)
xsUnknownError("bad name");
if ((tag > 63) || ((packetEnd - position) < tag))
break;
c_memcpy(tmp, position, tag);
xsmcSetStringBuffer(xsVar(2), tmp, tag);
xsCall1(xsVar(1), xsID_push, xsVar(2));
offset += tag;
position = offset + (uint8_t *)getPacket(the, NULL);
packet = (uint8_t *)getPacket(the, &packetEnd);
position = packet + offset;
}

return qnameEndPosition;
xsUnknownError("bad name");

return -1;
}

static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t answer)
Expand All @@ -149,10 +165,9 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
uint16_t qtype, qclass;
char tmp[256];

if (NULL == position) {
xsmcSetNull(xsResult);
xsmcSetNull(xsResult);
if (NULL == position)
return;
}

offset = position - (uint8_t *)getPacket(the, NULL);

Expand All @@ -163,7 +178,10 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
offset = parseQname(the, offset);
xsmcSet(xsVar(0), xsID_qname, xsVar(1));

position = offset + (uint8_t *)getPacket(the, NULL);
uint8_t *packetEnd;
position = offset + (uint8_t *)getPacket(the, &packetEnd);
if ((position + 4) > packetEnd)
return;

qtype = (position[0] << 8) | position[1];
qclass = (position[2] << 8) | position[3];
Expand All @@ -174,6 +192,8 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
uint32_t ttl;
uint16_t rdlength;

if ((position + 6) > packetEnd)
return;
ttl = (position[0] << 24) | (position[1] << 16) | (position[2] << 8) | position[3];
rdlength = (position[4] << 8) | position[5];

Expand All @@ -184,6 +204,8 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
if (0x0001 == qtype) { // A
uint8_t ip[4];
char *out;
if ((position + 4) > packetEnd)
return;
c_memcpy(ip, position, 4);
xsVar(1) = xsStringBuffer(NULL, 4 * 5);
out = xsmcToString(xsVar(1));
Expand Down Expand Up @@ -223,6 +245,9 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
else
#endif
if (0x0021 == qtype) { // SRV
if ((position + 6) > packetEnd)
return;

uint16_t priority = (position[0] << 8) | position[1];
uint16_t weight = (position[2] << 8) | position[3];
uint16_t port = (position[4] << 8) | position[5];
Expand All @@ -244,17 +269,23 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
if (0x0010 == qtype) { // TXT
if (rdlength > 1) {
xsVar(1) = xsNewArray(0);
position = offset + (uint8_t *)getPacket(the, NULL);
position = offset + (uint8_t *)getPacket(the, &packetEnd);
while (rdlength > 1) {
uint8_t tag;
if (position >= packetEnd)
return;

tag = *position++;
offset += tag + 1; //@@ bounds check range
if (rdlength < (uint16_t)(tag + 1))
return;
offset += tag + 1;
rdlength -= tag + 1;
if ((position + tag) > packetEnd)
return;
c_memcpy(tmp, position, tag);
xsmcSetStringBuffer(xsVar(2), tmp, tag);
xsCall1(xsVar(1), xsID_push, xsVar(2));
position = offset + (uint8_t *)getPacket(the, NULL);
position = offset + (uint8_t *)getPacket(the, &packetEnd);
}
xsmcSet(xsVar(0), xsID_rdata, xsVar(1));
}
Expand Down