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hysteria2: harden UDP datagram parsing against malformed input #145

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hysteria2: harden UDP datagram parsing against malformed input #145

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21 changes: 17 additions & 4 deletions src/hysteria2_server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -385,10 +385,15 @@ async fn run_udp_remote_to_local_loop(
// session_id(4) + packet_id(2) + fragment id(1) + fragment count(1) + address length varint + address bytes
let header_overhead = 4 + 2 + 1 + 1 + address_len_bytes.len() + address_bytes.len();

assert!(
max_datagram_size > header_overhead,
"max datagram size ({max_datagram_size}) is smaller than header overhead ({header_overhead})"
);
// `max_datagram_size` is reported by the remote QUIC endpoint and can be
// attacker-influenced; a value at/below the header overhead must not panic
// (and would underflow `max_datagram_size - header_overhead` below). Bail
// on this connection instead of asserting on remote input.
if max_datagram_size <= header_overhead {
return Err(std::io::Error::other(format!(
"datagram too small: max datagram size ({max_datagram_size}) <= header overhead ({header_overhead})"
)));
}

if header_overhead + payload_len <= max_datagram_size {
let mut datagram = BytesMut::with_capacity(header_overhead + payload_len);
Expand Down Expand Up @@ -489,6 +494,14 @@ async fn run_udp_local_to_remote_loop(
};
let mut next_index = 9;
if num_bytes > 1 {
// A small/truncated datagram could make this varint claim more
// bytes than are present; slicing past the end would panic on
// attacker-controlled input. Per the reference, malformed
// datagrams are ignored -- skip rather than crash.
if data.len() < 9 + (num_bytes - 1) {
debug!("Ignoring datagram with truncated varint address length");
continue;
}
let remaining = &data[9..9 + (num_bytes - 1)];
for byte in remaining {
value <<= 8;
Expand Down