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LibTLS: (Almost) verify certificate chain against root CA certificates

Also adds a very primitive systemwide ca_certs.ini file.
This commit is contained in:
AnotherTest 2020-10-30 11:56:31 +03:30 committed by Andreas Kling
parent 34f8d55100
commit 37c089fb7b
7 changed files with 632 additions and 4 deletions

View file

@ -28,6 +28,7 @@
#include <AK/ByteBuffer.h>
#include <AK/Forward.h>
#include <AK/Singleton.h>
#include <AK/Types.h>
#include <LibCrypto/BigInt/UnsignedBigInteger.h>
#include <LibCrypto/PK/RSA.h>
@ -77,6 +78,21 @@ struct Certificate {
bool is_valid() const;
};
class DefaultRootCACertificates {
public:
DefaultRootCACertificates();
const Vector<Certificate>& certificates() const { return m_ca_certificates; }
static DefaultRootCACertificates& the() { return s_the; }
private:
static AK::Singleton<DefaultRootCACertificates> s_the;
Vector<Certificate> m_ca_certificates;
};
}
using TLS::Certificate;
using TLS::DefaultRootCACertificates;

View file

@ -274,7 +274,14 @@ void TLSv12::build_random(PacketBuilder& builder)
m_context.premaster_key = ByteBuffer::copy(random_bytes, bytes);
const auto& certificate = m_context.certificates[0];
const auto& certificate_option = verify_chain_and_get_matching_certificate(m_context.SNI); // if the SNI is empty, we'll make a special case and match *a* leaf certificate.
if (!certificate_option.has_value()) {
dbg() << "certificate verification failed :(";
alert(AlertLevel::Critical, AlertDescription::BadCertificate);
return;
}
auto& certificate = m_context.certificates[certificate_option.value()];
#ifdef TLS_DEBUG
dbg() << "PreMaster secret";
print_buffer(m_context.premaster_key);

View file

@ -25,6 +25,7 @@
*/
#include <AK/Endian.h>
#include <LibCore/ConfigFile.h>
#include <LibCore/DateTime.h>
#include <LibCore/Timer.h>
#include <LibCrypto/ASN1/DER.h>
@ -498,8 +499,10 @@ ssize_t TLSv12::handle_certificate(const ByteBuffer& buffer)
auto certificate = parse_asn1(buffer.slice_view(res_cert, certificate_size_specific), false);
if (certificate.has_value()) {
m_context.certificates.append(certificate.value());
valid_certificate = true;
if (certificate.value().is_valid()) {
m_context.certificates.append(certificate.value());
valid_certificate = true;
}
}
res_cert += certificate_size_specific;
} while (remaining > 0);
@ -705,6 +708,94 @@ void TLSv12::try_disambiguate_error() const
}
}
void TLSv12::set_root_certificates(Vector<Certificate> certificates)
{
if (!m_context.root_ceritificates.is_empty())
dbg() << "TLS warn: resetting root certificates!";
for (auto& cert : certificates) {
if (!cert.is_valid())
dbg() << "Certificate for " << cert.subject << " by " << cert.issuer_subject << " is invalid, things may or may not work!";
// FIXME: Figure out what we should do when our root certs are invalid.
}
m_context.root_ceritificates = move(certificates);
}
bool Context::verify_chain() const
{
const Vector<Certificate>* local_chain = nullptr;
if (is_server) {
dbg() << "Unsupported: Server mode";
TODO();
} else {
local_chain = &certificates;
}
// FIXME: Actually verify the signature, instead of just checking the name.
HashMap<String, String> chain;
HashTable<String> roots;
// First, walk the root certs.
for (auto& cert : root_ceritificates) {
roots.set(cert.subject);
chain.set(cert.subject, cert.issuer_subject);
}
// Then, walk the local certs.
for (auto& cert : *local_chain) {
auto& issuer_unique_name = cert.issuer_unit.is_empty() ? cert.issuer_subject : cert.issuer_unit;
chain.set(cert.subject, issuer_unique_name);
}
// Then verify the chain.
for (auto& it : chain) {
if (it.key == it.value) { // Allow self-signed certificates.
if (!roots.contains(it.key))
dbg() << "Self-signed warning: Certificate for " << it.key << " is self-signed";
continue;
}
auto ref = chain.get(it.value);
if (!ref.has_value()) {
dbg() << "Certificate for " << it.key << " is not signed by anyone we trust (" << it.value << ")";
return false;
}
if (ref.value() == it.key) // Allow (but warn about) mutually recursively signed cert A <-> B.
dbg() << "Co-dependency warning: Certificate for " << ref.value() << " is issued by " << it.key << ", which itself is issued by " << ref.value();
}
return true;
}
static bool wildcard_matches(const StringView& host, const StringView& subject)
{
if (host.matches(subject))
return true;
if (subject.starts_with("*."))
return wildcard_matches(host, subject.substring_view(2));
return false;
}
Optional<size_t> TLSv12::verify_chain_and_get_matching_certificate(const StringView& host) const
{
if (m_context.certificates.is_empty() || !m_context.verify_chain())
return {};
if (host.is_empty())
return 0;
for (size_t i = 0; i < m_context.certificates.size(); ++i) {
auto& cert = m_context.certificates[i];
// FIXME: Also check against SAN (oid 2.5.29.17).
if (wildcard_matches(host, cert.subject))
return i;
}
return {};
}
TLSv12::TLSv12(Core::Object* parent, Version version)
: Core::Socket(Core::Socket::Type::TCP, parent)
{
@ -751,4 +842,18 @@ bool TLSv12::add_client_key(const ByteBuffer& certificate_pem_buffer, const Byte
return add_client_key(certificate);
}
AK::Singleton<DefaultRootCACertificates> DefaultRootCACertificates::s_the;
DefaultRootCACertificates::DefaultRootCACertificates()
{
// FIXME: This might not be the best format, find a better way to represent CA certificates.
auto config = Core::ConfigFile::get_for_system("ca_certs");
for (auto& entity : config->groups()) {
Certificate cert;
cert.subject = entity;
cert.issuer_subject = config->read_entry(entity, "issuer_subject", entity);
cert.country = config->read_entry(entity, "country");
m_ca_certificates.append(move(cert));
}
}
}

View file

@ -279,6 +279,8 @@ public:
bool load_certificates(const ByteBuffer& pem_buffer);
bool load_private_key(const ByteBuffer& pem_buffer);
void set_root_certificates(Vector<Certificate>);
bool add_client_key(const ByteBuffer& certificate_pem_buffer, const ByteBuffer& key_pem_buffer);
bool add_client_key(Certificate certificate)
{
@ -429,6 +431,8 @@ private:
bool compute_master_secret(size_t length);
Optional<size_t> verify_chain_and_get_matching_certificate(const StringView& host) const;
void try_disambiguate_error() const;
Context m_context;