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options/posix: add bound checks for dns response parsing #1190

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230 changes: 149 additions & 81 deletions options/posix/generic/lookup.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,40 +12,82 @@
#include <stdio.h>
#include <ctype.h>

namespace mlibc {

namespace {
constexpr unsigned int RECORD_A = 1;
constexpr unsigned int RECORD_CNAME = 5;
constexpr unsigned int RECORD_PTR = 12;
}

static frg::string<MemoryAllocator> read_dns_name(char *buf, char *&it) {
enum class DnsClass : uint16_t {
IN = 1,
};

enum class ResourceRecord : uint16_t {
A = 1,
NS = 2,
CNAME = 5,
PTR = 12,
TXT = 16,
AAAA = 28,
OPT = 41,
};

frg::optional<frg::string<MemoryAllocator>> read_dns_name(frg::span<uint8_t> buf, size_t &offset) {
frg::string<MemoryAllocator> res{getAllocator()};
while (true) {
char code = *it++;
if ((code & 0xC0) == 0xC0) {
while(offset < buf.size()) {
uint8_t code = buf[offset++];

if((code & 0xC0) == 0xC0) {
// pointer
uint8_t offset = ((code & 0x3F) << 8) | *it++;
auto offset_it = buf + offset;
return res + read_dns_name(buf, offset_it);
} else if (!(code & 0xC0)) {
if (!code)
break;
if(offset + 1 > buf.size()) {
return frg::null_opt;
}

uint8_t pointer_offset = ((code & 0x3F) << 8) | buf[offset++];
if(pointer_offset >= buf.size()) {
return frg::null_opt;
}

size_t sub_offset = pointer_offset;
auto sub_name = read_dns_name(buf, sub_offset);
if(!sub_name) {
return frg::null_opt;
}

return res + *sub_name;
} else if(!(code & 0xC0)) {
if (!code) {
return res;
} else if(offset + code > buf.size()) {
return frg::null_opt;
}

for (int i = 0; i < code; i++)
res += (*it++);
for (int i = 0; i < code; i++) {
res += buf[offset++];
}

if (*it)
if (offset < buf.size() && buf[offset]) {
res += '.';
}
} else {
break;
return frg::null_opt;
}
}

return res;
return frg::null_opt;
}

void writeUint16(frg::string<MemoryAllocator> &request, uint16_t val) {
request += static_cast<char>(val >> 8);
request += static_cast<char>(val & 0xFF);
};

uint16_t readUint16(frg::span<uint8_t> buf, size_t offset) {
uint16_t val = 0;
memcpy(&val, buf.data() + offset, sizeof(val));
return ntohs(val);
}

} // namespace

namespace mlibc {

int lookup_name_dns(struct lookup_result &buf, const char *name,
frg::string<MemoryAllocator> &canon_name) {
frg::string<MemoryAllocator> request{getAllocator()};
Expand Down Expand Up @@ -73,12 +115,8 @@ int lookup_name_dns(struct lookup_result &buf, const char *name,
}

request += char(0);
// set question type to fetch A records
request += 0;
request += 1;
// set CLASS to IN
request += 0;
request += 1;
writeUint16(request, static_cast<uint16_t>(ResourceRecord::A));
writeUint16(request, static_cast<uint16_t>(DnsClass::IN));

struct sockaddr_in sin = {};
sin.sin_family = AF_INET;
Expand All @@ -105,48 +143,69 @@ int lookup_name_dns(struct lookup_result &buf, const char *name,
return -EAI_SYSTEM;
}

char response[256];
uint8_t response[512];
ssize_t rlen;
int num_ans = 0;
while ((rlen = recvfrom(fd, response, 256, 0, NULL, NULL)) >= 0) {
while ((rlen = recvfrom(fd, response, sizeof(response), 0, NULL, NULL)) >= 0) {
if ((size_t)rlen < sizeof(struct dns_header))
continue;
auto response_header = reinterpret_cast<struct dns_header*>(response);
auto response_header = reinterpret_cast<struct dns_header *>(response);
if (response_header->identification != header.identification)
return -EAI_FAIL;

auto it = response + sizeof(struct dns_header);
auto view = frg::span<uint8_t>{response, static_cast<size_t>(rlen)};
size_t offset = sizeof(struct dns_header);

for (int i = 0; i < ntohs(response_header->no_q); i++) {
auto dns_name = read_dns_name(response, it);
(void) dns_name;
it += 4;
auto dns_name = read_dns_name(view, offset);
if(!dns_name)
return -EAI_FAIL;

// skip type and class
offset += 4;
}

for (int i = 0; i < ntohs(response_header->no_ans); i++) {
auto dns_name = read_dns_name(view, offset);
if(!dns_name) {
return -EAI_FAIL;
} else if(offset + 10 > view.size()) {
return -EAI_FAIL;
}

ResourceRecord rrType{readUint16(view, offset + 0)};
DnsClass rrClass{readUint16(view, offset + 2)};
// ignore TTL
uint16_t rrLength = readUint16(view, offset + 8);
offset += 10;

if(rrClass != DnsClass::IN || offset + rrLength > view.size()) {
return -EAI_FAIL;
}

struct dns_addr_buf buffer;
auto dns_name = read_dns_name(response, it);

uint16_t rr_type = (it[0] << 8) | it[1];
uint16_t rr_class = (it[2] << 8) | it[3];
uint16_t rr_length = (it[8] << 8) | it[9];
it += 10;
(void)rr_class;

switch (rr_type) {
case RECORD_A:
memcpy(buffer.addr, it, rr_length);
it += rr_length;
switch (rrType) {
case ResourceRecord::A:
memcpy(buffer.addr, &view[offset], rrLength);
offset += rrLength;
buffer.family = AF_INET;
buffer.name = std::move(dns_name);
buffer.name = std::move(*dns_name);
buf.buf.push(std::move(buffer));
break;
case RECORD_CNAME:
canon_name = read_dns_name(response, it);
buf.aliases.push(std::move(dns_name));
case ResourceRecord::CNAME: {
size_t suboffset = offset;
auto cname = read_dns_name(view, suboffset);
if(!cname) {
return -EAI_FAIL;
}
canon_name = std::move(*cname);
buf.aliases.push(std::move(*dns_name));
offset = suboffset;
break;
}
default:
mlibc::infoLogger() << "lookup_name_dns: unknown rr type "
<< rr_type << frg::endlog;
<< static_cast<uint16_t>(rrType) << frg::endlog;
break;
}
}
Expand Down Expand Up @@ -175,7 +234,7 @@ int lookup_addr_dns(frg::span<char> name, frg::array<uint8_t, 16> &addr, int fam
request.resize(sizeof(header));
memcpy(request.data(), &header, sizeof(header));

char addr_str[64];
char addr_str[INET6_ADDRSTRLEN];
if(!inet_ntop(family, addr.data(), addr_str, sizeof(addr_str))) {
switch(errno) {
case EAFNOSUPPORT:
Expand All @@ -201,13 +260,8 @@ int lookup_addr_dns(frg::span<char> name, frg::array<uint8_t, 16> &addr, int fam
} while(ptr != 0);

request += char(0);
// set question type to fetch PTR records
request += 0;
request += 12;
// set CLASS to IN
request += 0;
request += 1;

writeUint16(request, static_cast<uint16_t>(ResourceRecord::PTR));
writeUint16(request, static_cast<uint16_t>(DnsClass::IN));

struct sockaddr_in sin = {};
sin.sin_family = AF_INET;
Expand All @@ -234,48 +288,62 @@ int lookup_addr_dns(frg::span<char> name, frg::array<uint8_t, 16> &addr, int fam
return -EAI_SYSTEM;
}

char response[256];
uint8_t response[512];
ssize_t rlen;
int num_ans = 0;
while ((rlen = recvfrom(fd, response, 256, 0, NULL, NULL)) >= 0) {
while ((rlen = recvfrom(fd, response, sizeof(response), 0, NULL, NULL)) >= 0) {
if ((size_t)rlen < sizeof(struct dns_header))
continue;
auto response_header = reinterpret_cast<struct dns_header*>(response);
if (response_header->identification != header.identification)
return -EAI_FAIL;

auto it = response + sizeof(struct dns_header);
frg::span<uint8_t> view{response, static_cast<size_t>(rlen)};
size_t offset = sizeof(struct dns_header);

for (int i = 0; i < ntohs(response_header->no_q); i++) {
auto dns_name = read_dns_name(response, it);
(void) dns_name;
it += 4;
auto dns_name = read_dns_name(view, offset);
if(!dns_name)
return -EAI_FAIL;

offset += 4;
}

for (int i = 0; i < ntohs(response_header->no_ans); i++) {
struct dns_addr_buf buffer;
auto dns_name = read_dns_name(response, it);
auto dns_name = read_dns_name(view, offset);
if(!dns_name) {
return -EAI_FAIL;
} else if(offset + 10 > view.size()) {
return -EAI_FAIL;
}

uint16_t rr_type = (it[0] << 8) | it[1];
uint16_t rr_class = (it[2] << 8) | it[3];
uint16_t rr_length = (it[8] << 8) | it[9];
it += 10;
(void)rr_class;
(void)rr_length;
ResourceRecord rrType{readUint16(view, offset + 0)};
DnsClass rrClass{readUint16(view, offset + 2)};
// ignore TTL
uint16_t rrLength = readUint16(view, offset + 8);

(void)dns_name;
offset += 10;

switch (rr_type) {
case RECORD_PTR: {
auto ptr_name = read_dns_name(response, it);
if (ptr_name.size() >= name.size())
if(rrClass != DnsClass::IN || offset + rrLength > view.size()) {
return -EAI_FAIL;
}

struct dns_addr_buf buffer;
switch (rrType) {
case ResourceRecord::PTR: {
auto ptr_name = read_dns_name(view, offset);
if(!ptr_name) {
return -EAI_FAIL;
} else if(ptr_name->size() >= name.size()) {
return -EAI_OVERFLOW;
std::copy(ptr_name.begin(), ptr_name.end(), name.data());
name.data()[ptr_name.size()] = '\0';
}
std::copy(ptr_name->begin(), ptr_name->end(), name.data());
name.data()[ptr_name->size()] = '\0';
return 1;
}
default:
mlibc::infoLogger() << "lookup_addr_dns: unknown rr type "
<< rr_type << frg::endlog;
<< static_cast<uint16_t>(rrType) << frg::endlog;
break;
}
num_ans += ntohs(response_header->no_ans);
Expand Down
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