cluelessh/lib/cluelessh-transport/src/server.rs
2024-08-30 17:43:09 +02:00

601 lines
28 KiB
Rust

use std::{collections::VecDeque, mem::take};
use crate::crypto::{
self, AlgorithmName, EncryptionAlgorithm, HostKeySigningAlgorithm, KexAlgorithm, SharedSecret,
SupportedAlgorithms,
};
use crate::packet::{
KeyExchangeEcDhInitPacket, KeyExchangeInitPacket, Packet, PacketTransport, ProtocolIdentParser,
RecvBytesResult,
};
use crate::{peer_error, Msg, SshRng, SshStatus};
use crate::{Result, SessionId};
use cluelessh_format::numbers;
use cluelessh_format::{NameList, Reader, Writer};
use cluelessh_keys::private::PlaintextPrivateKey;
use cluelessh_keys::signature::Signature;
use tracing::{debug, info, trace};
pub struct ServerConnection {
state: ServerState,
packet_transport: PacketTransport,
rng: Box<dyn SshRng + Send + Sync>,
config: ServerConfig,
plaintext_packets: VecDeque<Packet>,
}
#[derive(Debug, Clone, Default)]
pub struct ServerConfig {
pub server_identification: Vec<u8>,
pub host_keys: Vec<cluelessh_keys::public::PublicKey>,
}
enum ServerState {
ProtoExchange {
ident_parser: ProtocolIdentParser,
},
KeyExchangeInit {
client_identification: Vec<u8>,
},
DhKeyInit {
client_identification: Vec<u8>,
client_kexinit: Vec<u8>,
server_kexinit: Vec<u8>,
kex_algorithm: crypto::KexAlgorithm,
server_host_key_algorithm: HostKeySigningAlgorithm,
encryption_client_to_server: EncryptionAlgorithm,
encryption_server_to_client: EncryptionAlgorithm,
},
WaitingForKeyExchange {
client_identification: Vec<u8>,
client_kexinit: Vec<u8>,
server_kexinit: Vec<u8>,
kex_algorithm: crypto::KexAlgorithm,
server_host_key_algorithm: HostKeySigningAlgorithm,
encryption_client_to_server: EncryptionAlgorithm,
encryption_server_to_client: EncryptionAlgorithm,
client_ephemeral_public_key: Vec<u8>,
},
NewKeys {
/// h
hash: [u8; 32],
/// k
shared_secret: SharedSecret,
encryption_client_to_server: EncryptionAlgorithm,
encryption_server_to_client: EncryptionAlgorithm,
},
ServiceRequest {
session_id: SessionId,
may_send_extensions: bool,
},
Open {
session_id: SessionId,
},
}
pub struct KeyExchangeParameters {
pub client_ident: Vec<u8>,
pub server_ident: Vec<u8>,
pub client_kexinit: Vec<u8>,
pub server_kexinit: Vec<u8>,
pub eph_client_public_key: Vec<u8>,
pub server_host_key_algorithm: HostKeySigningAlgorithm,
pub kex_algorithm: KexAlgorithm,
}
pub struct KeyExchangeResponse {
pub hash: SessionId,
pub server_ephemeral_public_key: Vec<u8>,
pub shared_secret: SharedSecret,
pub signature: Signature,
}
impl ServerConnection {
pub fn new(rng: impl SshRng + Send + Sync + 'static, config: ServerConfig) -> Self {
Self {
state: ServerState::ProtoExchange {
ident_parser: ProtocolIdentParser::new(),
},
packet_transport: PacketTransport::new(),
rng: Box::new(rng),
config,
plaintext_packets: VecDeque::new(),
}
}
pub fn recv_bytes(&mut self, mut bytes: &[u8]) -> Result<()> {
while let RecvBytesResult::Partial { consumed } = self.recv_bytes_inner(bytes)? {
bytes = &bytes[consumed..];
if bytes.is_empty() {
break;
}
}
Ok(())
}
fn recv_bytes_inner(&mut self, bytes: &[u8]) -> Result<RecvBytesResult> {
if let ServerState::ProtoExchange { ident_parser } = &mut self.state {
ident_parser.recv_bytes(bytes);
if let Some(client_identification) = ident_parser.get_peer_ident() {
self.packet_transport
.queue_send_protocol_info(self.config.server_identification.clone());
self.state = ServerState::KeyExchangeInit {
client_identification,
};
}
// This means that we must be called at least twice, which is fine I think.
return Ok(RecvBytesResult::Full);
}
let consumed = self.packet_transport.recv_bytes(bytes)?;
while let Some(packet) = self.packet_transport.recv_next_packet() {
let packet_type = packet.packet_type();
let packet_type_string = numbers::packet_type_to_string(packet_type);
trace!(%packet_type, %packet_type_string, packet_len = %packet.payload.len(), "Received packet");
// Handle some packets ignoring the state.
match packet_type {
numbers::SSH_MSG_DISCONNECT => {
// <https://datatracker.ietf.org/doc/html/rfc4253#section-11.1>
let mut disconnect = Reader::new(&packet.payload[1..]);
let reason = disconnect.u32()?;
let description = disconnect.utf8_string()?;
let _language_tag = disconnect.utf8_string()?;
let reason_string = numbers::disconnect_reason_to_string(reason);
debug!(%reason, %reason_string, %description, "Client disconnecting");
return Err(SshStatus::Disconnect);
}
numbers::SSH_MSG_IGNORE => {
// <https://datatracker.ietf.org/doc/html/rfc4253#section-11.2>
let mut p = Reader::new(&packet.payload[1..]);
let _ = p.string()?;
continue;
}
numbers::SSH_MSG_DEBUG => {
// <https://datatracker.ietf.org/doc/html/rfc4253#section-11.3>
let mut p = Reader::new(&packet.payload[1..]);
let always_display = p.bool()?;
let msg = p.utf8_string()?;
let _language_tag = p.utf8_string()?;
if always_display {
info!(%msg, "Received debug message (SSH_MSG_DEBUG)");
} else {
debug!(%msg, "Received debug message (SSH_MSG_DEBUG)")
}
continue;
}
_ => {}
}
match &mut self.state {
ServerState::ProtoExchange { .. } => unreachable!("handled above"),
ServerState::KeyExchangeInit {
client_identification,
} => {
let kex = KeyExchangeInitPacket::parse(&packet.payload)?;
let sup_algs = SupportedAlgorithms::secure(&self.config.host_keys);
let kex_algorithm = sup_algs.key_exchange.find(false, kex.kex_algorithms.0)?;
debug!(name = %kex_algorithm.name(), "Using KEX algorithm");
// <https://datatracker.ietf.org/doc/html/rfc8308#section-2.1>
// TODO: Send some extensions
// TODO: Because of the terrapin attack, we probably want to implement strict kex for that.
let _client_supports_extensions = kex.kex_algorithms.contains("ext-info-c");
let server_host_key_algorithm = sup_algs
.hostkey_sign
.find(false, kex.server_host_key_algorithms.0)?;
debug!(name = %server_host_key_algorithm.name(), "Using host key algorithm");
// TODO: Implement aes128-ctr
let _ = crypto::encrypt::ENC_AES128_CTR;
let encryption_client_to_server = sup_algs
.encryption_from_peer
.find(false, kex.encryption_algorithms_client_to_server.0)?;
debug!(name = %encryption_client_to_server.name(), "Using encryption algorithm C->S");
let encryption_server_to_client = sup_algs
.encryption_to_peer
.find(false, kex.encryption_algorithms_server_to_client.0)?;
debug!(name = %encryption_server_to_client.name(), "Using encryption algorithm S->C");
let mac_algorithm_client_to_server = sup_algs
.mac_from_peer
.find(false, kex.mac_algorithms_client_to_server.0)?;
let mac_algorithm_server_to_client = sup_algs
.mac_to_peer
.find(false, kex.mac_algorithms_server_to_client.0)?;
let compression_algorithm_client_to_server = sup_algs
.compression_from_peer
.find(false, kex.compression_algorithms_client_to_server.0)?;
let compression_algorithm_server_to_client = sup_algs
.compression_to_peer
.find(false, kex.compression_algorithms_server_to_client.0)?;
let _ = kex.languages_client_to_server;
let _ = kex.languages_server_to_client;
if kex.first_kex_packet_follows {
return Err(peer_error!(
"the client wants to send a guessed packet, that's annoying :("
));
}
let mut cookie = [0; 16];
self.rng.fill_bytes(&mut cookie);
// <https://datatracker.ietf.org/doc/html/rfc8308#section-2.1>
let kex_algorithms = format!("{},ext-info-s", kex_algorithm.name());
let server_kexinit = KeyExchangeInitPacket {
cookie,
// TODO: we should send *all* our algorithms here...
kex_algorithms: NameList::multi(&kex_algorithms),
server_host_key_algorithms: NameList::one(server_host_key_algorithm.name()),
encryption_algorithms_client_to_server: NameList::one(
encryption_client_to_server.name(),
),
encryption_algorithms_server_to_client: NameList::one(
encryption_server_to_client.name(),
),
mac_algorithms_client_to_server: NameList::one(
mac_algorithm_client_to_server,
),
mac_algorithms_server_to_client: NameList::one(
mac_algorithm_server_to_client,
),
compression_algorithms_client_to_server: NameList::one(
compression_algorithm_client_to_server,
),
compression_algorithms_server_to_client: NameList::one(
compression_algorithm_server_to_client,
),
languages_client_to_server: NameList::none(),
languages_server_to_client: NameList::none(),
first_kex_packet_follows: false,
};
let client_identification = take(client_identification);
let server_kexinit_payload = server_kexinit.to_bytes();
self.packet_transport.queue_packet(Packet {
payload: server_kexinit_payload.clone(),
});
self.state = ServerState::DhKeyInit {
client_identification,
client_kexinit: packet.payload,
server_kexinit: server_kexinit_payload,
kex_algorithm,
server_host_key_algorithm,
encryption_client_to_server,
encryption_server_to_client,
};
}
ServerState::DhKeyInit {
client_identification,
client_kexinit,
server_kexinit,
kex_algorithm,
server_host_key_algorithm,
encryption_client_to_server,
encryption_server_to_client,
} => {
let dh = KeyExchangeEcDhInitPacket::parse(&packet.payload)?;
let client_ephemeral_public_key = dh.qc;
self.state = ServerState::WaitingForKeyExchange {
client_identification: client_identification.clone(),
client_kexinit: client_kexinit.clone(),
server_kexinit: server_kexinit.clone(),
kex_algorithm: *kex_algorithm,
server_host_key_algorithm: server_host_key_algorithm.clone(),
encryption_client_to_server: *encryption_client_to_server,
encryption_server_to_client: *encryption_server_to_client,
client_ephemeral_public_key: client_ephemeral_public_key.to_vec(),
};
}
ServerState::WaitingForKeyExchange { .. } => {
return Err(peer_error!("unexpected packet"));
}
ServerState::NewKeys {
hash: h,
shared_secret: k,
encryption_client_to_server,
encryption_server_to_client,
} => {
if packet.payload != [numbers::SSH_MSG_NEWKEYS] {
return Err(peer_error!("did not send SSH_MSG_NEWKEYS"));
}
self.packet_transport.queue_packet(Packet {
payload: vec![numbers::SSH_MSG_NEWKEYS],
});
self.packet_transport.set_key(
*h,
k,
*encryption_client_to_server,
*encryption_server_to_client,
true,
);
self.state = ServerState::ServiceRequest {
session_id: SessionId(*h),
may_send_extensions: true, // TODO: false if the client didn't advertise them
};
}
ServerState::ServiceRequest {
session_id,
may_send_extensions,
} => match packet_type {
numbers::SSH_MSG_SERVICE_REQUEST => {
let mut p = packet.payload_parser();
p.u8()?;
let service = p.utf8_string()?;
debug!(%service, "Client requesting service");
if service != "ssh-userauth" {
return Err(peer_error!("only supports ssh-userauth"));
}
self.packet_transport.queue_packet(Packet {
payload: {
let mut writer = Writer::new();
writer.u8(numbers::SSH_MSG_SERVICE_ACCEPT);
writer.string(service.as_bytes());
writer.finish()
},
});
self.state = ServerState::Open {
session_id: *session_id,
};
}
numbers::SSH_MSG_EXT_INFO if *may_send_extensions => {
let mut p = packet.payload_parser();
p.u8()?;
let count = p.u32()?;
debug!(%count, "Received extensions");
for _ in 0..count {
// while the spec doesn't say it, if you send an extension name that's invalid UTF-8 you deserve the error
let name = p.utf8_string()?;
let _value = p.string()?;
debug!(?name, "Received extension");
}
self.state = ServerState::ServiceRequest {
session_id: *session_id,
may_send_extensions: false,
};
}
_ => {
return Err(peer_error!(
"unexpected packet: {packet_type}, expected SSH_MSG_SERVICE_REQUEST"
))
}
},
ServerState::Open { .. } => {
self.plaintext_packets.push_back(packet);
}
}
}
Ok(consumed)
}
pub fn is_open(&self) -> Option<SessionId> {
match self.state {
ServerState::Open { session_id } => Some(session_id),
_ => None,
}
}
pub fn is_waiting_on_key_exchange(&self) -> Option<KeyExchangeParameters> {
match &self.state {
ServerState::WaitingForKeyExchange {
client_identification,
client_kexinit,
server_kexinit,
kex_algorithm,
server_host_key_algorithm,
client_ephemeral_public_key,
..
} => Some(KeyExchangeParameters {
client_ident: client_identification.clone(),
server_ident: self.config.server_identification.to_vec(),
client_kexinit: client_kexinit.clone(),
server_kexinit: server_kexinit.clone(),
eph_client_public_key: client_ephemeral_public_key.clone(),
server_host_key_algorithm: server_host_key_algorithm.clone(),
kex_algorithm: *kex_algorithm,
}),
_ => None,
}
}
pub fn do_key_exchange(&mut self, response: KeyExchangeResponse) {
match &self.state {
ServerState::WaitingForKeyExchange {
encryption_client_to_server,
encryption_server_to_client,
server_host_key_algorithm,
..
} => {
let packet = Packet::new_msg_kex_ecdh_reply(
&server_host_key_algorithm.public_key().to_wire_encoding(),
&response.server_ephemeral_public_key,
&response.signature.to_wire_encoding(),
);
self.packet_transport.queue_packet(packet);
self.state = ServerState::NewKeys {
hash: response.hash.0,
shared_secret: response.shared_secret.clone(),
encryption_client_to_server: *encryption_client_to_server,
encryption_server_to_client: *encryption_server_to_client,
};
}
_ => unreachable!("doing signature while not waiting for it"),
}
}
pub fn next_msg_to_send(&mut self) -> Option<Msg> {
self.packet_transport.next_msg_to_send()
}
pub fn next_plaintext_packet(&mut self) -> Option<Packet> {
self.plaintext_packets.pop_front()
}
pub fn send_plaintext_packet(&mut self, packet: Packet) {
self.packet_transport.queue_packet(packet);
}
}
pub fn do_key_exchange(
msg: KeyExchangeParameters,
private: &PlaintextPrivateKey,
rng: &mut dyn SshRng,
) -> Result<KeyExchangeResponse> {
let server_secret = (msg.kex_algorithm.generate_secret)(rng);
let server_ephemeral_public_key = server_secret.pubkey;
let shared_secret = (server_secret.exchange)(&msg.eph_client_public_key)?;
let pub_hostkey = msg.server_host_key_algorithm.public_key();
let hash = crypto::key_exchange_hash(
&msg.client_ident,
&msg.server_ident,
&msg.client_kexinit,
&msg.server_kexinit,
&pub_hostkey.to_wire_encoding(),
&msg.eph_client_public_key,
&server_ephemeral_public_key,
&shared_secret,
);
Ok(KeyExchangeResponse {
hash: SessionId(hash),
server_ephemeral_public_key,
shared_secret,
signature: private.private_key.sign(&hash),
})
}
#[cfg(test)]
mod tests {
use hex_literal::hex;
use crate::{
packet::MsgKind,
server::{ServerConfig, ServerConnection},
SshRng,
};
struct NoRng;
impl SshRng for NoRng {
fn fill_bytes(&mut self, _: &mut [u8]) {
unreachable!()
}
}
struct HardcodedRng(Vec<u8>);
impl SshRng for HardcodedRng {
fn fill_bytes(&mut self, dest: &mut [u8]) {
dest.copy_from_slice(&self.0[..dest.len()]);
self.0.splice(0..dest.len(), []);
}
}
#[test]
fn protocol_exchange() {
let mut con = ServerConnection::new(NoRng, ServerConfig::default());
con.recv_bytes(b"SSH-2.0-OpenSSH_9.7\r\n").unwrap();
let msg = con.next_msg_to_send().unwrap();
assert!(matches!(msg.0, MsgKind::ServerProtocolInfo(_)));
}
#[test]
fn protocol_exchange_slow_client() {
let mut con = ServerConnection::new(NoRng, ServerConfig::default());
con.recv_bytes(b"SSH-2.0-").unwrap();
con.recv_bytes(b"OpenSSH_9.7\r\n").unwrap();
let msg = con.next_msg_to_send().unwrap();
assert!(matches!(msg.0, MsgKind::ServerProtocolInfo(_)));
}
#[test]
#[ignore = "this is super annoying, use expect-test please"]
fn handshake() {
#[rustfmt::skip]
let rng = vec![
0x14, 0xa2, 0x04, 0xa5, 0x4b, 0x2f, 0x5f, 0xa7, 0xff, 0x53, 0x13, 0x67, 0x57, 0x67, 0xbc,
0x55, 0x3f, 0xc0, 0x6c, 0x0d, 0x07, 0x8f, 0xe2, 0x75, 0x95, 0x18, 0x4b, 0xd2, 0xcb, 0xd0,
0x64, 0x06, 0x14, 0xa2, 0x04, 0xa5, 0x4b, 0x2f, 0x5f, 0xa7, 0xff, 0x53, 0x13, 0x67, 0x57,
0x67, 0xbc, 0x55, 0x3f, 0xc0, 0x6c, 0x0d, 0x07, 0x8f, 0xe2, 0x75, 0x95, 0x18, 0x4b, 0xd2,
0xcb, 0xd0, 0x64, 0x06, 0x67, 0xbc, 0x55, 0x3f, 0xc0, 0x6c, 0x0d, 0x07, 0x8f, 0xe2, 0x75,
0x95, 0x18, 0x4b, 0xd2, 0xcb, 0xd0, 0x64, 0x06,
];
struct Part {
client: &'static [u8],
server: &'static [u8],
}
// Extracted from a real OpenSSH client using this server (with hardcoded creds) using Wireshark.
let conversation = [
Part {
client: &hex!("5353482d322e302d4f70656e5353485f392e370d0a"),
server: &hex!("5353482d322e302d4f70656e5353485f392e370d0a"),
},
// KEX Init
Part {
client: &hex!(
"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"
),
server: &hex!(
"000000bc051414a204a54b2f5fa7ff5313675767bc5500000011637572766532353531392d7368613235360000000b7373682d656432353531390000001d63686163686132302d706f6c7931333035406f70656e7373682e636f6d0000001d63686163686132302d706f6c7931333035406f70656e7373682e636f6d0000000d686d61632d736861322d3235360000000d686d61632d736861322d323536000000046e6f6e65000000046e6f6e65000000000000000000000000000000000000"
),
},
// ECDH KEX Init
Part {
client: &hex!(
"0000002c061e000000204c646d1281abf23264d63db96e05c0223cfead668d9d38c62579b8856e67ae19000000000000"
),
server: &hex!(
"000000bc081f000000330000000b7373682d6564323535313900000020e939cdfa6fc0d737333b534e913dd332c8d5179fe00c3045575217224b19b8f6000000204260e2c5e5383f1a021c9631fa61f60f305b29183fd219d4c8207c664e063410000000530000000b7373682d65643235353139000000406504a045499f26aa4ee17606ea6bd9e3f288838591f25d8604a63f77a52f5b9e909c00d10f386553e585d86ab329bbde0fca5c64b1b1982d7adcac17cf7f06010000000000000000"
),
},
// New Keys
Part {
client: &hex!("0000000c0a1500000000000000000000"),
server: &hex!("0000000c0a1500000000000000000000"),
},
// Service Request (encrypted)
Part {
client: &hex!("09ca4db7baeb24836a1f7d22368055bf4c26981ed86738ac7a5c31d0730ad656f1967853781dff91ee1c4de8"),
server: &hex!("7b444c0d5faf740d350701a054ea469fab1c98e4b669e4872a454163edb42ec5e4fa95c404ab601f016bd259"),
},
];
let mut con = ServerConnection::new(HardcodedRng(rng), ServerConfig::default());
for part in conversation {
con.recv_bytes(&part.client).unwrap();
eprintln!("client: {:x?}", part.client);
let bytes = con.next_msg_to_send().unwrap().to_bytes();
if part.server != bytes {
panic!(
"expected != found\nexpected: {:x?}\nfound: {:x?}",
part.server, bytes
);
}
}
}
}