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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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62 changes: 46 additions & 16 deletions modules/network/dns/moddnsparser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,10 @@ static void *getQuestionByIndex(xsMachine *the, uint8_t index)
position += 12;
while (index--) {
while (true) {
uint8_t tag = *position++;
uint8_t tag;
if (position >= packetEnd)
return NULL;
tag = *position++;
if (0 == tag)
break;
if (0xC0 == (tag & 0xC0)) {
Expand Down Expand Up @@ -85,7 +88,10 @@ static void *getAnswerByIndex(xsMachine *the, uint8_t index)
uint16_t rdlength;

while (true) {
uint8_t tag = *position++;
uint8_t tag;
if (position >= packetEnd)
return NULL;
tag = *position++;
if (0 == tag)
break;
if (0xC0 == (tag & 0xC0)) {
Expand All @@ -109,35 +115,45 @@ static void *getAnswerByIndex(xsMachine *the, uint8_t index)

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

xsVar(1) = xsNewArray(0);
position = offset + (uint8_t *)getPacket(the, NULL);;
position = offset + packet;
while (true) {
char tmp[64];
uint8_t tag = *position++;
uint8_t tag;
if (position >= packetEnd)
xsUnknownError("bad name");
tag = *position++;
offset += 1;
if (0 == tag) {
if (0 == qnameEndPosition)
qnameEndPosition = offset;
break;
}
if (0xC0 == (tag & 0xC0)) {
if (position >= packetEnd)
xsUnknownError("bad name");
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 (offset >= packetEnd - packet)
xsUnknownError("bad name");
position = offset + packet;
continue;
}

if (tag > 63)
xsUnknownError("bad name");
if (position + tag > packetEnd)
xsUnknownError("bad name");
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);
position = offset + packet;
}

return qnameEndPosition;
Expand All @@ -148,13 +164,15 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
int offset;
uint16_t qtype, qclass;
char tmp[256];
uint8_t *packet, *packetEnd;

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

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

xsmcVars(4);

Expand All @@ -163,8 +181,10 @@ 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);
position = offset + packet;

if (position + 4 > packetEnd)
xsUnknownError("bad name");
qtype = (position[0] << 8) | position[1];
qclass = (position[2] << 8) | position[3];
position += 4;
Expand All @@ -174,16 +194,22 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
uint32_t ttl;
uint16_t rdlength;

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

position += 6;
offset += 6;

if (position + rdlength > packetEnd)
xsUnknownError("bad name");
if (rdlength) {
if (0x0001 == qtype) { // A
uint8_t ip[4];
char *out;
if (position + 4 > packetEnd)
xsUnknownError("bad name");
c_memcpy(ip, position, 4);
xsVar(1) = xsStringBuffer(NULL, 4 * 5);
out = xsmcToString(xsVar(1));
Expand Down Expand Up @@ -223,9 +249,12 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
else
#endif
if (0x0021 == qtype) { // SRV
uint16_t priority = (position[0] << 8) | position[1];
uint16_t weight = (position[2] << 8) | position[3];
uint16_t port = (position[4] << 8) | position[5];
uint16_t priority, weight, port;
if (position + 6 > packetEnd)
xsUnknownError("bad name");
priority = (position[0] << 8) | position[1];
weight = (position[2] << 8) | position[3];
port = (position[4] << 8) | position[5];
offset += 6;

xsVar(3) = xsNewObject();
Expand All @@ -246,10 +275,11 @@ static void parseQuestionOrAnswer(xsMachine *the, uint8_t *position, uint8_t ans
xsVar(1) = xsNewArray(0);
position = offset + (uint8_t *)getPacket(the, NULL);
while (rdlength > 1) {
uint8_t tag;
uint8_t tag = *position++;

tag = *position++;
offset += tag + 1; //@@ bounds check range
if (tag + 1 > rdlength)
break;
offset += tag + 1;
rdlength -= tag + 1;
c_memcpy(tmp, position, tag);
xsmcSetStringBuffer(xsVar(2), tmp, tag);
Expand Down