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keysend: enforce BOLT11 description length limit #8535

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keysend: enforce BOLT11 description length limit #8535

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3 changes: 2 additions & 1 deletion plugins/keysend.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
#include <ccan/asort/asort.h>
#include <ccan/cast/cast.h>
#include <ccan/tal/str/str.h>
#include <common/bolt11.h>
#include <common/gossmap.h>
#include <common/json_param.h>
#include <common/json_stream.h>
Expand Down Expand Up @@ -563,7 +564,7 @@ static struct command_result *htlc_accepted_call(struct command *cmd,
(const char *)desc_field->value);
json_add_string(req->js, "description", desc);
/* Don't exceed max possible desc length! */
if (strlen(desc) > 1023)
if (strlen(desc) >= BOLT11_FIELD_BYTE_LIMIT)
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Should this be > or >=? lightningd/invoice.c uses >, however the BOLT11 spec says:

Note that the maximum length of a Tagged Field's data is constricted by the maximum value of data_length. This is 1023 x 5 bits, or 639 bytes.

In common/bolt11.c BOLT11_FIELD_BYTE_LIMIT has a value of 640.

Far from an expert here and appreciate any insight. Happy to update as needed.

json_add_bool(req->js, "deschashonly", true);
} else {
json_add_string(req->js, "description", "keysend");
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25 changes: 25 additions & 0 deletions tests/test_pay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
tu64_encode
)
import copy
import json
import os
import pytest
import random
Expand Down Expand Up @@ -3697,6 +3698,30 @@ def test_keysend_maxfee(node_factory):
assert len(l3.rpc.listinvoices()['invoices']) == 1


@pytest.mark.parametrize("tlv_payload_length", [638, 639, 640, 641, 1022, 1023, 1024])
def test_keysend_description_size_limit(node_factory, tlv_payload_length):
"""
Test keysend description handling near BOLT11 field size limits.

Checks boundary conditions where the payload length is just below,
exactly at, and just above the maximum allowed tagged-field size.

See common/bolt11.h: BOLT11_FIELD_BYTE_LIMIT.
"""
l1, l2 = node_factory.line_graph(2, wait_for_announce=True)
amt = 10000
prefix = 'keysend: {"message": ""}'
base_len = len(prefix)

# Prep TLV payload with test length
body_len = tlv_payload_length - base_len
tlv_payload = json.dumps({"message": "a" * body_len}).encode().hex()

# Send keysend payment with test payload
l1.rpc.keysend(l2.info["id"], amt, extratlvs={7629169: tlv_payload})
assert len(l2.rpc.listinvoices()["invoices"]) == 1


def test_invalid_onion_channel_update(node_factory):
'''
Some onion failures "should" send a `channel_update`.
Expand Down
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