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Code Issues Releases Wiki Activity

dns: bad label size interpreted as decompression pointer (#466)

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Co-authored-by: Bill Willcox <billwcorp@gmail.com>
This commit is contained in:
Bill Willcox
2022-02-20 18:18:00 -05:00
committed by GitHub
parent 54e4e4b0f4
commit c302e659d7
2 changed files with 52 additions and 1 deletions
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2
src/dns.cpp
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@@ -342,7 +342,7 @@ uint32_t DNS::compose_name(const uint8_t* ptr, char* out_ptr) const {
throw dns_decompression_pointer_loops();
}
// It's an offset
if ((*ptr & 0xc0)) {
if (((*ptr & 0xc0) == 0xc0)) {
if (TINS_UNLIKELY(ptr + sizeof(uint16_t) > end)) {
throw malformed_packet();
}

51
tests/src/dns_test.cpp
View File

@@ -551,3 +551,54 @@ TEST_F(DNSTest, SOARecordSerialize) {
EXPECT_EQ(0x8ad71928U, r2.expire());
EXPECT_EQ(0x1ad92871U, r2.minimum_ttl());
}
TEST_F(DNSTest, BadLabelSize) {
const uint8_t header[] = {
0x45, 0xbc, // ID
0x81, 0x80, // response, recursion desired, recursion available, no error
0x00, 0x01, // QDCOUNT
0x00, 0x00, // ANCOUNT
0x00, 0x00, // NSCOUNT
0x00, 0x00 // ARCOUNT
};
size_t payload_sz{sizeof(header)};
uint8_t payload[512];
// copy header
std::copy(header,
header + payload_sz,
payload);
// add bad length
const size_t bad_label_len{0x80};
payload[payload_sz++] = bad_label_len;
// fill label for incorrect length and terminate
std::fill(payload + payload_sz,
payload + payload_sz + bad_label_len,
'a');
payload_sz += bad_label_len;
payload[payload_sz++] = 0x0;
// add type and class
const uint8_t type_class[] = {
0x00, 0x01,
0x00, 0x01
};
std::copy(type_class,
type_class + sizeof(type_class),
payload + payload_sz);
payload_sz += sizeof(type_class);
// SUCCEED moves from dns_decompression_pointer_out_of_bounds to malformed_packet after fix
const DNS packet(payload, payload_sz);
EXPECT_EQ(packet.questions_count(), 1);
try {
const auto queries{packet.queries()};
FAIL();
} catch (dns_decompression_pointer_out_of_bounds& oob) {
FAIL();
} catch (malformed_packet& mp) {
SUCCEED();
}
}