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Log cases where an onion failure cannot be attributed or interpreted #3629

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Log cases where an onion failure cannot be attributed or interpreted #3629

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447148d
Add test coverage for process_onion_failure
joostjager Feb 28, 2025
f307ab7
Remove error side effect from decrypt_onion_error_packet
joostjager Mar 3, 2025
00f42de
Log cases where an onion failure cannot be attributed or interpreted
joostjager Feb 28, 2025
f38244c
Properly attribute unreadable failures with a valid hmac
joostjager Feb 28, 2025
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277 changes: 232 additions & 45 deletions lightning/src/ln/onion_utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -931,15 +931,11 @@ pub(crate) struct DecodedOnionFailure {
pub(crate) onion_error_data: Option<Vec<u8>>,
}

/// Note that we always decrypt `packet` in-place here even if the deserialization into
/// [`msgs::DecodedOnionErrorPacket`] ultimately fails.
fn decrypt_onion_error_packet(
packet: &mut Vec<u8>, shared_secret: SharedSecret,
) -> Result<msgs::DecodedOnionErrorPacket, msgs::DecodeError> {
/// Decrypt the error packet in-place.
fn decrypt_onion_error_packet(packet: &mut Vec<u8>, shared_secret: SharedSecret) {
let ammag = gen_ammag_from_shared_secret(shared_secret.as_ref());
let mut chacha = ChaCha20::new(&ammag, &[0u8; 8]);
chacha.process_in_place(packet);
msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(packet))
}

/// Process failure we got back from upstream on a payment we sent (implying htlc_source is an
Expand Down Expand Up @@ -1021,9 +1017,11 @@ where
{
// Actually parse the onion error data in tests so we can check that blinded hops fail
// back correctly.
let err_packet =
decrypt_onion_error_packet(&mut encrypted_packet, shared_secret)
.unwrap();
decrypt_onion_error_packet(&mut encrypted_packet, shared_secret);
let err_packet = msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(
&encrypted_packet,
))
.unwrap();
error_code_ret = Some(u16::from_be_bytes(
err_packet.failuremsg.get(0..2).unwrap().try_into().unwrap(),
));
Expand All @@ -1044,22 +1042,44 @@ where
let amt_to_forward = htlc_msat - route_hop.fee_msat;
htlc_msat = amt_to_forward;

let err_packet = match decrypt_onion_error_packet(&mut encrypted_packet, shared_secret) {
Ok(p) => p,
Err(_) => return,
};
decrypt_onion_error_packet(&mut encrypted_packet, shared_secret);

let um = gen_um_from_shared_secret(shared_secret.as_ref());
let mut hmac = HmacEngine::<Sha256>::new(&um);
hmac.input(&err_packet.encode()[32..]);
hmac.input(&encrypted_packet[32..]);

if !fixed_time_eq(&Hmac::from_engine(hmac).to_byte_array(), &err_packet.hmac) {
if !fixed_time_eq(&Hmac::from_engine(hmac).to_byte_array(), &encrypted_packet[..32]) {
return;
}

let err_packet =
match msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(&encrypted_packet)) {
Ok(p) => p,
Err(_) => {
log_warn!(logger, "Unreadable failure from {}", route_hop.pubkey);

let network_update = Some(NetworkUpdate::NodeFailure {
node_id: route_hop.pubkey,
is_permanent: true,
});
let short_channel_id = Some(route_hop.short_channel_id);
res = Some(FailureLearnings {
network_update,
short_channel_id,
payment_failed_permanently: is_from_final_node,
failed_within_blinded_path: false,
});
return;
},
};

let error_code_slice = match err_packet.failuremsg.get(0..2) {
Some(s) => s,
None => {
// Useless packet that we can't use but it passed HMAC, so it definitely came from the peer
// in question
log_warn!(logger, "Missing error code in failure from {}", route_hop.pubkey);

let network_update = Some(NetworkUpdate::NodeFailure {
node_id: route_hop.pubkey,
is_permanent: true,
Expand Down Expand Up @@ -1219,6 +1239,12 @@ where
} else {
// only not set either packet unparseable or hmac does not match with any
// payment not retryable only when garbage is from the final node
log_warn!(
logger,
"Non-attributable failure encountered on route {}",
path.hops.iter().map(|h| h.pubkey.to_string()).collect::<Vec<_>>().join("->")
);

DecodedOnionFailure {
network_update: None,
short_channel_id: None,
Expand Down Expand Up @@ -1764,7 +1790,10 @@ fn decode_next_hop<T, R: ReadableArgs<T>, N: NextPacketBytes>(

#[cfg(test)]
mod tests {
use std::sync::Arc;

use crate::io;
use crate::ln::channelmanager::PaymentId;
use crate::ln::msgs;
use crate::routing::router::{Path, PaymentParameters, Route, RouteHop};
use crate::types::features::{ChannelFeatures, NodeFeatures};
Expand All @@ -1773,6 +1802,7 @@ mod tests {

#[allow(unused_imports)]
use crate::prelude::*;
use crate::util::test_utils::TestLogger;

use bitcoin::hex::FromHex;
use bitcoin::secp256k1::Secp256k1;
Expand All @@ -1785,40 +1815,95 @@ mod tests {
SecretKey::from_slice(&<Vec<u8>>::from_hex(hex).unwrap()[..]).unwrap()
}

fn build_test_path() -> Path {
Path {
hops: vec![
RouteHop {
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rustfmt wanted this

pubkey: PublicKey::from_slice(
&<Vec<u8>>::from_hex(
"02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619",
)
.unwrap()[..],
)
.unwrap(),
channel_features: ChannelFeatures::empty(),
node_features: NodeFeatures::empty(),
short_channel_id: 0,
fee_msat: 0,
cltv_expiry_delta: 0,
maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(
&<Vec<u8>>::from_hex(
"0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c",
)
.unwrap()[..],
)
.unwrap(),
channel_features: ChannelFeatures::empty(),
node_features: NodeFeatures::empty(),
short_channel_id: 1,
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it is a move, but just these short_channel_id's made unique to make it easier to test things for attr errors

fee_msat: 0,
cltv_expiry_delta: 0,
maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(
&<Vec<u8>>::from_hex(
"027f31ebc5462c1fdce1b737ecff52d37d75dea43ce11c74d25aa297165faa2007",
)
.unwrap()[..],
)
.unwrap(),
channel_features: ChannelFeatures::empty(),
node_features: NodeFeatures::empty(),
short_channel_id: 2,
fee_msat: 0,
cltv_expiry_delta: 0,
maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(
&<Vec<u8>>::from_hex(
"032c0b7cf95324a07d05398b240174dc0c2be444d96b159aa6c7f7b1e668680991",
)
.unwrap()[..],
)
.unwrap(),
channel_features: ChannelFeatures::empty(),
node_features: NodeFeatures::empty(),
short_channel_id: 3,
fee_msat: 0,
cltv_expiry_delta: 0,
maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(
&<Vec<u8>>::from_hex(
"02edabbd16b41c8371b92ef2f04c1185b4f03b6dcd52ba9b78d9d7c89c8f221145",
)
.unwrap()[..],
)
.unwrap(),
channel_features: ChannelFeatures::empty(),
node_features: NodeFeatures::empty(),
short_channel_id: 4,
fee_msat: 0,
cltv_expiry_delta: 0,
maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
],
blinded_tail: None,
}
}

fn build_test_onion_keys() -> Vec<OnionKeys> {
// Keys from BOLT 4, used in both test vector tests
let secp_ctx = Secp256k1::new();

let route = Route {
paths: vec![Path { hops: vec![
RouteHop {
pubkey: PublicKey::from_slice(&<Vec<u8>>::from_hex("02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619").unwrap()[..]).unwrap(),
channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
short_channel_id: 0, fee_msat: 0, cltv_expiry_delta: 0, maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(&<Vec<u8>>::from_hex("0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c").unwrap()[..]).unwrap(),
channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
short_channel_id: 0, fee_msat: 0, cltv_expiry_delta: 0, maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(&<Vec<u8>>::from_hex("027f31ebc5462c1fdce1b737ecff52d37d75dea43ce11c74d25aa297165faa2007").unwrap()[..]).unwrap(),
channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
short_channel_id: 0, fee_msat: 0, cltv_expiry_delta: 0, maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(&<Vec<u8>>::from_hex("032c0b7cf95324a07d05398b240174dc0c2be444d96b159aa6c7f7b1e668680991").unwrap()[..]).unwrap(),
channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
short_channel_id: 0, fee_msat: 0, cltv_expiry_delta: 0, maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
RouteHop {
pubkey: PublicKey::from_slice(&<Vec<u8>>::from_hex("02edabbd16b41c8371b92ef2f04c1185b4f03b6dcd52ba9b78d9d7c89c8f221145").unwrap()[..]).unwrap(),
channel_features: ChannelFeatures::empty(), node_features: NodeFeatures::empty(),
short_channel_id: 0, fee_msat: 0, cltv_expiry_delta: 0, maybe_announced_channel: true, // We fill in the payloads manually instead of generating them from RouteHops.
},
], blinded_tail: None }],
route_params: None,
};
let path = build_test_path();
let route = Route { paths: vec![path], route_params: None };

let onion_keys =
super::construct_onion_keys(&secp_ctx, &route.paths[0], &get_test_session_key())
Expand Down Expand Up @@ -2078,6 +2163,108 @@ mod tests {
);
let hex = "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";
assert_eq!(onion_packet_5.data, <Vec<u8>>::from_hex(hex).unwrap());

let logger: Arc<TestLogger> = Arc::new(TestLogger::new());
let ctx_full = Secp256k1::new();
let path = build_test_path();
let htlc_source = HTLCSource::OutboundRoute {
path,
session_priv: get_test_session_key(),
first_hop_htlc_msat: 0,
payment_id: PaymentId([1; 32]),
};

// Assert that the original failure can be retrieved and that all hmacs check out.
let decrypted_failure =
process_onion_failure(&ctx_full, &logger, &htlc_source, onion_packet_5.data);

assert_eq!(decrypted_failure.onion_error_code, Some(0x2002));
}

#[test]
fn test_non_attributable_failure_packet_onion() {
// Create a failure packet with bogus data.
let packet = vec![1u8; 292];

// In the current protocol, it is unfortunately not possible to identify the failure source.
let logger: TestLogger = TestLogger::new();
let decrypted_failure = test_failure_attribution(&logger, &packet);
assert_eq!(decrypted_failure.short_channel_id, None);

logger.assert_log_contains(
"lightning::ln::onion_utils",
"Non-attributable failure encountered",
1,
);
}

#[test]
fn test_unreadable_failure_packet_onion() {
// Create a failure packet with a valid hmac but unreadable failure message.
let onion_keys: Vec<OnionKeys> = build_test_onion_keys();
let shared_secret = onion_keys[0].shared_secret.as_ref();
let um = gen_um_from_shared_secret(&shared_secret);

// The failure message is a single 0 byte.
let mut packet = [0u8; 33];

let mut hmac = HmacEngine::<Sha256>::new(&um);
hmac.input(&packet[32..]);
let hmac = Hmac::from_engine(hmac).to_byte_array();
packet[..32].copy_from_slice(&hmac);

let packet = encrypt_failure_packet(shared_secret, &packet);

// For the unreadable failure, it is still expected that the failing channel can be identified.
let logger: TestLogger = TestLogger::new();
let decrypted_failure = test_failure_attribution(&logger, &packet.data);
assert_eq!(decrypted_failure.short_channel_id, Some(0));

logger.assert_log_contains("lightning::ln::onion_utils", "Unreadable failure", 1);
}

#[test]
fn test_missing_error_code() {
// Create a failure packet with a valid hmac and structure, but no error code.
let onion_keys: Vec<OnionKeys> = build_test_onion_keys();
let shared_secret = onion_keys[0].shared_secret.as_ref();
let um = gen_um_from_shared_secret(&shared_secret);

let failuremsg = vec![1];
let pad = Vec::new();
let mut packet = msgs::DecodedOnionErrorPacket { hmac: [0; 32], failuremsg, pad };

let mut hmac = HmacEngine::<Sha256>::new(&um);
hmac.input(&packet.encode()[32..]);
packet.hmac = Hmac::from_engine(hmac).to_byte_array();

let packet = encrypt_failure_packet(shared_secret, &packet.encode()[..]);

let logger = TestLogger::new();
let decrypted_failure = test_failure_attribution(&logger, &packet.data);
assert_eq!(decrypted_failure.short_channel_id, Some(0));

logger.assert_log_contains(
"lightning::ln::onion_utils",
"Missing error code in failure",
1,
);
}

fn test_failure_attribution(logger: &TestLogger, packet: &[u8]) -> DecodedOnionFailure {
let ctx_full = Secp256k1::new();
let path = build_test_path();
let htlc_source = HTLCSource::OutboundRoute {
path,
session_priv: get_test_session_key(),
first_hop_htlc_msat: 0,
payment_id: PaymentId([1; 32]),
};

let decrypted_failure =
process_onion_failure(&ctx_full, &logger, &htlc_source, packet.into());

decrypted_failure
}

struct RawOnionHopData {
Expand Down
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