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

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

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114 changes: 79 additions & 35 deletions options/posix/generic/lookup.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,30 +20,49 @@ namespace {
constexpr unsigned int RECORD_PTR = 12;
}

static frg::string<MemoryAllocator> read_dns_name(char *buf, char *&it) {
static frg::optional<frg::string<MemoryAllocator>> read_dns_name(uint8_t *buf,
size_t buf_size, uint8_t *&it) {
frg::string<MemoryAllocator> res{getAllocator()};
while (true) {
char code = *it++;
if ((code & 0xC0) == 0xC0) {
while(it < buf + buf_size) {
uint8_t code = *it++;
if((code & 0xC0) == 0xC0) {
// pointer
if(it + 1 > buf + buf_size) {
return frg::null_opt;
}

uint8_t offset = ((code & 0x3F) << 8) | *it++;
if(offset >= buf_size) {
return frg::null_opt;
}

auto offset_it = buf + offset;
return res + read_dns_name(buf, offset_it);
} else if (!(code & 0xC0)) {
if (!code)
break;
auto sub_name = read_dns_name(buf, buf_size, offset_it);
if(!sub_name) {
return frg::null_opt;
}

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

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

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

return res;
return frg::null_opt;
}

int lookup_name_dns(struct lookup_result &buf, const char *name,
Expand Down Expand Up @@ -105,10 +124,10 @@ int lookup_name_dns(struct lookup_result &buf, const char *name,
return -EAI_SYSTEM;
}

char response[256];
uint8_t response[1500];
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);
Expand All @@ -117,33 +136,48 @@ int lookup_name_dns(struct lookup_result &buf, const char *name,

auto it = response + 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;
auto dns_name = read_dns_name(response, sizeof(response), it);
if(!dns_name) {
return -EAI_FAIL;
}
it += 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(response, sizeof(response), it);
if(!dns_name) {
return -EAI_FAIL;
} else if(it + 10 > response + rlen) {
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;
if(it + rr_length > response + rlen) {
return -EAI_FAIL;
}

struct dns_addr_buf buffer;
switch (rr_type) {
case RECORD_A:
memcpy(buffer.addr, it, rr_length);
it += rr_length;
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 RECORD_CNAME: {
auto cname = read_dns_name(response, sizeof(response), it);
if(!cname) {
return -EAI_FAIL;
}
canon_name = std::move(*cname);
buf.aliases.push(std::move(*dns_name));
break;
}
default:
mlibc::infoLogger() << "lookup_name_dns: unknown rr type "
<< rr_type << frg::endlog;
Expand Down Expand Up @@ -234,10 +268,10 @@ 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[1500];
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);
Expand All @@ -246,31 +280,41 @@ int lookup_addr_dns(frg::span<char> name, frg::array<uint8_t, 16> &addr, int fam

auto it = response + 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;
auto dns_name = read_dns_name(response, sizeof(response), it);
if(!dns_name) {
return -EAI_FAIL;
}
it += 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(response, sizeof(response), it);
if(!dns_name) {
return -EAI_FAIL;
} else if(it + 10 > response + rlen) {
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;

(void)dns_name;
if(it + rr_length > response + rlen) {
return -EAI_FAIL;
}

struct dns_addr_buf buffer;
switch (rr_type) {
case RECORD_PTR: {
auto ptr_name = read_dns_name(response, it);
if (ptr_name.size() >= name.size())
auto ptr_name = read_dns_name(response, sizeof(response), it);
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:
Expand Down
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