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Defer DTLS handshake consumption until parse succeeds #144

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61 changes: 51 additions & 10 deletions src/dtls12/message/handshake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,13 +13,16 @@ use super::HelloVerifyRequest;
use super::ServerHello;
use super::ServerKeyExchange;
use crate::buffer::Buf;
use arrayvec::ArrayVec;
use nom::Err;
use nom::IResult;
use nom::bytes::complete::take;
use nom::error::{Error, ErrorKind};
use nom::number::complete::be_u8;
use nom::number::complete::{be_u16, be_u24};

const MAX_DEFRAGMENT_HANDSHAKES: usize = 50;

#[derive(Debug, PartialEq, Eq, Default, Clone, Copy)]
pub struct Header {
pub msg_type: MessageType,
Expand Down Expand Up @@ -154,8 +157,11 @@ impl Handshake {
let Body::Fragment(range) = &first_handshake.body else {
unreachable!("Non-Fragment body in defragment()")
};
let mut handled = ArrayVec::<&Handshake, MAX_DEFRAGMENT_HANDSHAKES>::new();
handled
.try_push(first_handshake)
.map_err(|_| crate::InternalError::too_many_records())?;
buffer.extend_from_slice(&first_buffer[range.clone()]);
first_handshake.set_handled();

for (handshake, source_buf) in iter {
if handshake.header.msg_type != first_handshake.header.msg_type {
Expand All @@ -166,7 +172,9 @@ impl Handshake {
unreachable!("Non-Fragment body in defragment()")
};

handshake.handled.store(true, Ordering::Relaxed);
handled
.try_push(handshake)
.map_err(|_| crate::InternalError::too_many_records())?;

buffer.extend_from_slice(&source_buf[range.clone()]);
}
Expand All @@ -176,7 +184,18 @@ impl Handshake {
return Err(crate::InternalError::parse_incomplete());
}

// If transcript is provided, write the handshake header + body before parsing
let (rest, body) = Body::parse(buffer, 0, first_handshake.header.msg_type, cipher_suite)?;

if !rest.is_empty() && first_handshake.header.msg_type == MessageType::Finished {
debug!("Defragmentation failed. Body::parse() did not consume the entire buffer");
return Err(crate::InternalError::parse_incomplete());
}

for handshake in handled {
handshake.set_handled();
}

// If transcript is provided, write the handshake header + body after parsing succeeds.
if let Some(transcript) = transcript {
transcript.push(first_handshake.header.msg_type.as_u8());
transcript.extend_from_slice(&first_handshake.header.length.to_be_bytes()[1..]);
Expand All @@ -187,13 +206,6 @@ impl Handshake {
transcript.extend_from_slice(&buffer[..first_handshake.header.length as usize]);
}

let (rest, body) = Body::parse(buffer, 0, first_handshake.header.msg_type, cipher_suite)?;

if !rest.is_empty() && first_handshake.header.msg_type == MessageType::Finished {
debug!("Defragmentation failed. Body::parse() did not consume the entire buffer");
return Err(crate::InternalError::parse_incomplete());
}

let handshake = Handshake {
header: Header {
msg_type: first_handshake.header.msg_type,
Expand Down Expand Up @@ -695,4 +707,33 @@ mod tests {

assert!(rest.is_empty());
}

#[test]
fn failed_defragment_parse_does_not_mark_handshake_or_write_transcript() {
let mut body = MESSAGE[12..].to_vec();
body[38] = 0;
body[39] = 3;

let handshake = Handshake::new(
MessageType::ClientHello,
body.len() as u32,
0,
0,
body.len() as u32,
Body::Fragment(0..body.len()),
);

let mut defragmented_buffer = Buf::new();
let mut transcript = Buf::new();
let result = Handshake::defragment(
std::iter::once((&handshake, body.as_slice())),
&mut defragmented_buffer,
None,
Some(&mut transcript),
);

assert!(result.is_err());
assert!(!handshake.is_handled());
assert!(transcript.is_empty());
}
}
39 changes: 27 additions & 12 deletions src/dtls13/message/handshake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,13 +5,16 @@ use std::sync::atomic::{AtomicBool, Ordering};
use super::{Certificate, CertificateVerify, ClientHello, Dtls13CipherSuite};
use super::{EncryptedExtensions, Finished, ServerHello};
use crate::buffer::Buf;
use arrayvec::ArrayVec;
use nom::Err;
use nom::IResult;
use nom::bytes::complete::take;
use nom::error::{Error, ErrorKind};
use nom::number::complete::be_u8;
use nom::number::complete::{be_u16, be_u24};

const MAX_DEFRAGMENT_HANDSHAKES: usize = 50;

#[derive(Debug, PartialEq, Eq, Default, Clone, Copy)]
pub struct Header {
pub msg_type: MessageType,
Expand Down Expand Up @@ -165,8 +168,11 @@ impl Handshake {
let Body::Fragment(range) = &first_handshake.body else {
unreachable!("Non-Fragment body in defragment()")
};
let mut handled = ArrayVec::<&Handshake, MAX_DEFRAGMENT_HANDSHAKES>::new();
handled
.try_push(first_handshake)
.map_err(|_| crate::InternalError::too_many_records())?;
buffer.extend_from_slice(&first_buffer[range.clone()]);
first_handshake.set_handled();

let mut assembled_end =
first_handshake.header.fragment_offset + first_handshake.header.fragment_length;
Expand All @@ -180,7 +186,9 @@ impl Handshake {
unreachable!("Non-Fragment body in defragment()")
};

handshake.handled.store(true, Ordering::Relaxed);
handled
.try_push(handshake)
.map_err(|_| crate::InternalError::too_many_records())?;

// Handle overlapping fragment data: skip bytes already assembled
let frag_start = handshake.header.fragment_offset as usize;
Expand All @@ -200,15 +208,6 @@ impl Handshake {
return Err(crate::InternalError::parse_incomplete());
}

// If transcript is provided, write the TLS 1.3-style header + body.
// Per RFC 9147 Section 5.2, the transcript uses msg_type(1) + length(3)
// WITHOUT the DTLS-specific message_seq, fragment_offset, fragment_length.
if let Some(transcript) = transcript {
transcript.push(first_handshake.header.msg_type.as_u8());
transcript.extend_from_slice(&first_handshake.header.length.to_be_bytes()[1..]);
transcript.extend_from_slice(&buffer[..first_handshake.header.length as usize]);
}

let (rest, body) = if allow_unknown_client_hello_suites {
Body::parse_allow_unknown_client_hello_suites(
buffer,
Expand All @@ -225,6 +224,19 @@ impl Handshake {
return Err(crate::InternalError::parse_incomplete());
}

for handshake in handled {
handshake.set_handled();
}

// If transcript is provided, write the TLS 1.3-style header + body after parsing succeeds.
// Per RFC 9147 Section 5.2, the transcript uses msg_type(1) + length(3)
// WITHOUT the DTLS-specific message_seq, fragment_offset, fragment_length.
if let Some(transcript) = transcript {
transcript.push(first_handshake.header.msg_type.as_u8());
transcript.extend_from_slice(&first_handshake.header.length.to_be_bytes()[1..]);
transcript.extend_from_slice(&buffer[..first_handshake.header.length as usize]);
}

let handshake = Handshake {
header: Header {
msg_type: first_handshake.header.msg_type,
Expand Down Expand Up @@ -619,16 +631,19 @@ mod tests {
);

let mut buffer = Buf::new();
let mut transcript = Buf::new();
let result = Handshake::defragment(
std::iter::once((&handshake, source.as_slice())),
&mut buffer,
None,
None,
Some(&mut transcript),
);

assert!(
result.is_err(),
"KeyUpdate bodies with trailing bytes must be rejected"
);
assert!(!handshake.is_handled());
assert!(transcript.is_empty());
}
}
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