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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// This file implements functions necessary for address validation.
use std::{
net::{IpAddr, SocketAddr},
time::{Duration, Instant},
};
use neqo_common::{qinfo, qtrace, Decoder, Encoder, Role};
use neqo_crypto::{
constants::{TLS_AES_128_GCM_SHA256, TLS_VERSION_1_3},
selfencrypt::SelfEncrypt,
};
use smallvec::SmallVec;
use crate::{
cid::ConnectionId, packet::PacketBuilder, recovery::RecoveryToken, stats::FrameStats, Res,
};
/// A prefix we add to Retry tokens to distinguish them from `NEW_TOKEN` tokens.
const TOKEN_IDENTIFIER_RETRY: &[u8] = &[0x52, 0x65, 0x74, 0x72, 0x79];
/// A prefix on `NEW_TOKEN` tokens, that is maximally Hamming distant from `NEW_TOKEN`.
/// Together, these need to have a low probability of collision, even if there is
/// corruption of individual bits in transit.
const TOKEN_IDENTIFIER_NEW_TOKEN: &[u8] = &[0xad, 0x9a, 0x8b, 0x8d, 0x86];
/// The maximum number of tokens we'll save from `NEW_TOKEN` frames.
/// This should be the same as the value of `MAX_TICKETS` in neqo-crypto.
const MAX_NEW_TOKEN: usize = 4;
/// The number of tokens we'll track for the purposes of looking for duplicates.
/// This is based on how many might be received over a period where could be
/// retransmissions. It should be at least `MAX_NEW_TOKEN`.
const MAX_SAVED_TOKENS: usize = 8;
/// `ValidateAddress` determines what sort of address validation is performed.
/// In short, this determines when a Retry packet is sent.
#[derive(Debug, PartialEq, Eq)]
pub enum ValidateAddress {
/// Require address validation never.
Never,
/// Require address validation unless a `NEW_TOKEN` token is provided.
NoToken,
/// Require address validation even if a `NEW_TOKEN` token is provided.
Always,
}
pub enum AddressValidationResult {
Pass,
ValidRetry(ConnectionId),
Validate,
Invalid,
}
pub struct AddressValidation {
/// What sort of validation is performed.
validation: ValidateAddress,
/// A self-encryption object used for protecting Retry tokens.
self_encrypt: SelfEncrypt,
/// When this object was created.
start_time: Instant,
}
impl AddressValidation {
pub fn new(now: Instant, validation: ValidateAddress) -> Res<Self> {
Ok(Self {
validation,
self_encrypt: SelfEncrypt::new(TLS_VERSION_1_3, TLS_AES_128_GCM_SHA256)?,
start_time: now,
})
}
fn encode_aad(peer_address: SocketAddr, retry: bool) -> Encoder {
// Let's be "clever" by putting the peer's address in the AAD.
// We don't need to encode these into the token as they should be
// available when we need to check the token.
let mut aad = Encoder::default();
if retry {
aad.encode(TOKEN_IDENTIFIER_RETRY);
} else {
aad.encode(TOKEN_IDENTIFIER_NEW_TOKEN);
}
match peer_address.ip() {
IpAddr::V4(a) => {
aad.encode_byte(4);
aad.encode(&a.octets());
}
IpAddr::V6(a) => {
aad.encode_byte(6);
aad.encode(&a.octets());
}
}
if retry {
aad.encode_uint(2, peer_address.port());
}
aad
}
pub fn generate_token(
&self,
dcid: Option<&ConnectionId>,
peer_address: SocketAddr,
now: Instant,
) -> Res<Vec<u8>> {
const EXPIRATION_RETRY: Duration = Duration::from_secs(5);
const EXPIRATION_NEW_TOKEN: Duration = Duration::from_secs(60 * 60 * 24);
// TODO(mt) rotate keys on a fixed schedule.
let retry = dcid.is_some();
let mut data = Encoder::default();
let end = now
+ if retry {
EXPIRATION_RETRY
} else {
EXPIRATION_NEW_TOKEN
};
let end_millis = u32::try_from(end.duration_since(self.start_time).as_millis())?;
data.encode_uint(4, end_millis);
if let Some(dcid) = dcid {
data.encode(dcid);
}
// Include the token identifier ("Retry"/~) in the AAD, then keep it for plaintext.
let mut buf = Self::encode_aad(peer_address, retry);
let encrypted = self.self_encrypt.seal(buf.as_ref(), data.as_ref())?;
buf.truncate(TOKEN_IDENTIFIER_RETRY.len());
buf.encode(&encrypted);
Ok(buf.into())
}
/// This generates a token for use with Retry.
pub fn generate_retry_token(
&self,
dcid: &ConnectionId,
peer_address: SocketAddr,
now: Instant,
) -> Res<Vec<u8>> {
self.generate_token(Some(dcid), peer_address, now)
}
/// This generates a token for use with `NEW_TOKEN`.
pub fn generate_new_token(&self, peer_address: SocketAddr, now: Instant) -> Res<Vec<u8>> {
self.generate_token(None, peer_address, now)
}
pub fn set_validation(&mut self, validation: ValidateAddress) {
qtrace!("AddressValidation {:p}: set to {:?}", self, validation);
self.validation = validation;
}
/// Decrypts `token` and returns the connection ID it contains.
/// Returns a tuple with a boolean indicating whether this thinks
/// that the token was a Retry token, and a connection ID, that is
/// None if the token wasn't successfully decrypted.
fn decrypt_token(
&self,
token: &[u8],
peer_address: SocketAddr,
retry: bool,
now: Instant,
) -> Option<ConnectionId> {
let peer_addr = Self::encode_aad(peer_address, retry);
let data = self.self_encrypt.open(peer_addr.as_ref(), token).ok()?;
let mut dec = Decoder::new(&data);
match dec.decode_uint(4) {
Some(d) => {
let end = self.start_time + Duration::from_millis(d);
if end < now {
qtrace!("Expired token: {:?} vs. {:?}", end, now);
return None;
}
}
_ => return None,
}
Some(ConnectionId::from(dec.decode_remainder()))
}
/// Calculate the Hamming difference between our identifier and the target.
/// Less than one difference per byte indicates that it is likely not a Retry.
/// This generous interpretation allows for a lot of damage in transit.
/// Note that if this check fails, then the token will be treated like it came
/// from `NEW_TOKEN` instead. If there truly is corruption of packets that causes
/// validation failure, it will be a failure that we try to recover from.
fn is_likely_retry(token: &[u8]) -> bool {
let mut difference = 0;
for i in 0..TOKEN_IDENTIFIER_RETRY.len() {
difference += (token[i] ^ TOKEN_IDENTIFIER_RETRY[i]).count_ones();
}
usize::try_from(difference).unwrap() < TOKEN_IDENTIFIER_RETRY.len()
}
pub fn validate(
&self,
token: &[u8],
peer_address: SocketAddr,
now: Instant,
) -> AddressValidationResult {
qtrace!(
"AddressValidation {:p}: validate {:?}",
self,
self.validation
);
if token.is_empty() {
if self.validation == ValidateAddress::Never {
qinfo!("AddressValidation: no token; accepting");
return AddressValidationResult::Pass;
}
qinfo!("AddressValidation: no token; validating");
return AddressValidationResult::Validate;
}
if token.len() <= TOKEN_IDENTIFIER_RETRY.len() {
// Treat bad tokens strictly.
qinfo!("AddressValidation: too short token");
return AddressValidationResult::Invalid;
}
let retry = Self::is_likely_retry(token);
let enc = &token[TOKEN_IDENTIFIER_RETRY.len()..];
// Note that this allows the token identifier part to be corrupted.
// That's OK here as we don't depend on that being authenticated.
if let Some(cid) = self.decrypt_token(enc, peer_address, retry, now) {
if retry {
// This is from Retry, so we should have an ODCID >= 8.
if cid.len() >= 8 {
qinfo!("AddressValidation: valid Retry token for {}", cid);
AddressValidationResult::ValidRetry(cid)
} else {
panic!("AddressValidation: Retry token with small CID {cid}");
}
} else if cid.is_empty() {
// An empty connection ID means NEW_TOKEN.
if self.validation == ValidateAddress::Always {
qinfo!("AddressValidation: valid NEW_TOKEN token; validating again");
AddressValidationResult::Validate
} else {
qinfo!("AddressValidation: valid NEW_TOKEN token; accepting");
AddressValidationResult::Pass
}
} else {
panic!("AddressValidation: NEW_TOKEN token with CID {cid}");
}
} else {
// From here on, we have a token that we couldn't decrypt.
// We've either lost the keys or we've received junk.
if retry {
// If this looked like a Retry, treat it as being bad.
qinfo!("AddressValidation: invalid Retry token; rejecting");
AddressValidationResult::Invalid
} else if self.validation == ValidateAddress::Never {
// We don't require validation, so OK.
qinfo!("AddressValidation: invalid NEW_TOKEN token; accepting");
AddressValidationResult::Pass
} else {
// This might be an invalid NEW_TOKEN token, or a valid one
// for which we have since lost the keys. Check again.
qinfo!("AddressValidation: invalid NEW_TOKEN token; validating again");
AddressValidationResult::Validate
}
}
}
}
// Note: these lint override can be removed in later versions where the lints
// either don't trip a false positive or don't apply. rustc 1.46 is fine.
#[allow(dead_code, clippy::large_enum_variant)]
pub enum NewTokenState {
Client {
/// Tokens that haven't been taken yet.
pending: SmallVec<[Vec<u8>; MAX_NEW_TOKEN]>,
/// Tokens that have been taken, saved so that we can discard duplicates.
old: SmallVec<[Vec<u8>; MAX_SAVED_TOKENS]>,
},
Server(NewTokenSender),
}
impl NewTokenState {
pub fn new(role: Role) -> Self {
match role {
Role::Client => Self::Client {
pending: SmallVec::<[_; MAX_NEW_TOKEN]>::new(),
old: SmallVec::<[_; MAX_SAVED_TOKENS]>::new(),
},
Role::Server => Self::Server(NewTokenSender::default()),
}
}
/// Is there a token available?
pub fn has_token(&self) -> bool {
match self {
Self::Client { ref pending, .. } => !pending.is_empty(),
Self::Server(..) => false,
}
}
/// If this is a client, take a token if there is one.
/// If this is a server, panic.
pub fn take_token(&mut self) -> Option<&[u8]> {
if let Self::Client {
ref mut pending,
ref mut old,
} = self
{
if let Some(t) = pending.pop() {
if old.len() >= MAX_SAVED_TOKENS {
old.remove(0);
}
old.push(t);
Some(&old[old.len() - 1])
} else {
None
}
} else {
unreachable!();
}
}
/// If this is a client, save a token.
/// If this is a server, panic.
pub fn save_token(&mut self, token: Vec<u8>) {
if let Self::Client {
ref mut pending,
ref old,
} = self
{
for t in old.iter().rev().chain(pending.iter().rev()) {
if t == &token {
qinfo!("NewTokenState discarding duplicate NEW_TOKEN");
return;
}
}
if pending.len() >= MAX_NEW_TOKEN {
pending.remove(0);
}
pending.push(token);
} else {
unreachable!();
}
}
/// If this is a server, maybe send a frame.
/// If this is a client, do nothing.
pub fn write_frames(
&mut self,
builder: &mut PacketBuilder,
tokens: &mut Vec<RecoveryToken>,
stats: &mut FrameStats,
) {
if let Self::Server(ref mut sender) = self {
sender.write_frames(builder, tokens, stats);
}
}
/// If this a server, buffer a `NEW_TOKEN` for sending.
/// If this is a client, panic.
pub fn send_new_token(&mut self, token: Vec<u8>) {
if let Self::Server(ref mut sender) = self {
sender.send_new_token(token);
} else {
unreachable!();
}
}
/// If this a server, process a lost signal for a `NEW_TOKEN` frame.
/// If this is a client, panic.
pub fn lost(&mut self, seqno: usize) {
if let Self::Server(ref mut sender) = self {
sender.lost(seqno);
} else {
unreachable!();
}
}
/// If this a server, process remove the acknowledged `NEW_TOKEN` frame.
/// If this is a client, panic.
pub fn acked(&mut self, seqno: usize) {
if let Self::Server(ref mut sender) = self {
sender.acked(seqno);
} else {
unreachable!();
}
}
}
struct NewTokenFrameStatus {
seqno: usize,
token: Vec<u8>,
needs_sending: bool,
}
impl NewTokenFrameStatus {
fn len(&self) -> usize {
1 + Encoder::vvec_len(self.token.len())
}
}
#[derive(Default)]
pub struct NewTokenSender {
/// The unacknowledged `NEW_TOKEN` frames we are yet to send.
tokens: Vec<NewTokenFrameStatus>,
/// A sequence number that is used to track individual tokens
/// by reference (so that recovery tokens can be simple).
next_seqno: usize,
}
impl NewTokenSender {
/// Add a token to be sent.
pub fn send_new_token(&mut self, token: Vec<u8>) {
self.tokens.push(NewTokenFrameStatus {
seqno: self.next_seqno,
token,
needs_sending: true,
});
self.next_seqno += 1;
}
pub fn write_frames(
&mut self,
builder: &mut PacketBuilder,
tokens: &mut Vec<RecoveryToken>,
stats: &mut FrameStats,
) {
for t in &mut self.tokens {
if t.needs_sending && t.len() <= builder.remaining() {
t.needs_sending = false;
builder.encode_varint(crate::frame::FRAME_TYPE_NEW_TOKEN);
builder.encode_vvec(&t.token);
tokens.push(RecoveryToken::NewToken(t.seqno));
stats.new_token += 1;
}
}
}
pub fn lost(&mut self, seqno: usize) {
for t in &mut self.tokens {
if t.seqno == seqno {
t.needs_sending = true;
break;
}
}
}
pub fn acked(&mut self, seqno: usize) {
self.tokens.retain(|i| i.seqno != seqno);
}
}
#[cfg(test)]
mod tests {
use neqo_common::Role;
use super::NewTokenState;
const ONE: &[u8] = &[1, 2, 3];
const TWO: &[u8] = &[4, 5];
#[test]
fn duplicate_saved() {
let mut tokens = NewTokenState::new(Role::Client);
tokens.save_token(ONE.to_vec());
tokens.save_token(TWO.to_vec());
tokens.save_token(ONE.to_vec());
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably TWO
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably ONE
assert!(!tokens.has_token());
assert!(tokens.take_token().is_none());
}
#[test]
fn duplicate_after_take() {
let mut tokens = NewTokenState::new(Role::Client);
tokens.save_token(ONE.to_vec());
tokens.save_token(TWO.to_vec());
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably TWO
tokens.save_token(ONE.to_vec());
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably ONE
assert!(!tokens.has_token());
assert!(tokens.take_token().is_none());
}
#[test]
fn duplicate_after_empty() {
let mut tokens = NewTokenState::new(Role::Client);
tokens.save_token(ONE.to_vec());
tokens.save_token(TWO.to_vec());
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably TWO
assert!(tokens.has_token());
assert!(tokens.take_token().is_some()); // probably ONE
tokens.save_token(ONE.to_vec());
assert!(!tokens.has_token());
assert!(tokens.take_token().is_none());
}
}