ssh-agent-client-rs 1.1.3

use crate::Error::UnknownMessageType;
use crate::codec::ReadMessage::{Failure, Success};
use crate::{Error, Identity, Result};
use bytes::{Buf, Bytes, BytesMut};
use ssh_encoding::{Decode, Encode};
use ssh_key::{Algorithm, Certificate, PrivateKey, PublicKey, Signature};
use std::io::{ErrorKind, Read, Write};

type MessageTypeId = u8;
// This list is copied from
// https://datatracker.ietf.org/doc/html/draft-miller-ssh-agent-04#section-5.1
const SSH_AGENTC_REQUEST_IDENTITIES: MessageTypeId = 11;
const SSH_AGENTC_SIGN_REQUEST: MessageTypeId = 13;
const SSH_AGENTC_ADD_IDENTITY: MessageTypeId = 17;
const SSH_AGENTC_REMOVE_IDENTITY: MessageTypeId = 18;
const SSH_AGENTC_REMOVE_ALL_IDENTITIES: MessageTypeId = 19;

const SSH_AGENT_FAILURE: MessageTypeId = 5;
const SSH_AGENT_SUCCESS: MessageTypeId = 6;
const SSH_AGENT_SIGN_RESPONSE: MessageTypeId = 14;
const SSH_AGENT_IDENTITIES_ANSWER: MessageTypeId = 12;

// This list is copied from
// https://datatracker.ietf.org/doc/html/draft-miller-ssh-agent-04#section-7.3
const SSH_AGENT_RSA_SHA2_512: usize = 0x04;

// to avoid allocating far too much memory
const MAX_MESSAGE_SIZE: usize = 1024 * 1024;

// since we allocate memory for our Vec of identities up front, let's have a high value
// but one that doesn't make us allocate enough memory for the Vec for it to become a
// denial of service issue
const MAX_IDENTITY_COUNT: usize = 1024;

//#[repr(u8)]
pub enum WriteMessage<'a> {
    RequestIdentities,
    Sign(&'a Identity<'a>, &'a [u8]),
    AddIdentity(&'a PrivateKey),
    RemoveIdentity(&'a PrivateKey),
    RemoveAllIdentities,
}

#[derive(Debug)]
pub enum ReadMessage {
    Failure,
    Success,
    Identities(Vec<Identity<'static>>),
    Signature(Signature),
}

pub fn read_message(input: &mut dyn Read) -> Result<ReadMessage> {
    let (t, buf) = read_packet(input)?;
    match t {
        SSH_AGENT_FAILURE => Ok(Failure),
        SSH_AGENT_SUCCESS => Ok(Success),
        SSH_AGENT_IDENTITIES_ANSWER => Ok(ReadMessage::Identities(make_identities(buf)?)),
        SSH_AGENT_SIGN_RESPONSE => {
            // Discard the first 4 bytes, as they just encode the length of the field
            let mut buf = &buf[..];
            if buf.get_length()? != buf.len() {
                return invalid_data("different inner and outer size");
            }
            let sig = Signature::decode(&mut buf)?;
            Ok(ReadMessage::Signature(sig))
        }
        _ => Err(UnknownMessageType(t)),
    }
}

pub fn write_message(output: &mut dyn Write, message: WriteMessage) -> Result<()> {
    let mut buf: Vec<u8> = Vec::new();
    match message {
        WriteMessage::RequestIdentities => buf.write_all(&[SSH_AGENTC_REQUEST_IDENTITIES])?,
        WriteMessage::AddIdentity(key) => {
            buf.write_all(&[SSH_AGENTC_ADD_IDENTITY])?;
            key.key_data().encode(&mut buf)?;

            let comment = key.comment();
            write_u32(comment.len(), &mut buf)?;
            buf.write_all(comment.as_ref())?
        }
        WriteMessage::RemoveIdentity(key) => {
            buf.write_all(&[SSH_AGENTC_REMOVE_IDENTITY])?;
            write_u32(key.public_key().key_data().encoded_len()?, &mut buf)?;
            key.public_key().key_data().encode(&mut buf)?;
        }
        WriteMessage::RemoveAllIdentities => buf.write_all(&[SSH_AGENTC_REMOVE_ALL_IDENTITIES])?,
        WriteMessage::Sign(key, data) => {
            match key {
                Identity::PublicKey(key) => {
                    buf.write_all(&[SSH_AGENTC_SIGN_REQUEST])?;
                    write_u32(key.key_data().encoded_len()?, &mut buf)?;
                    key.key_data().encode(&mut buf)?;
                    write_u32(data.len(), &mut buf)?;
                    buf.write_all(data)?;
                    // Emit signature flags, see the spec section 4.5.1
                    match key.algorithm() {
                        // Let's always use the SHA2 512-bit hash when signing RSA keys, to simplify the API
                        Algorithm::Rsa { hash: _ } => write_u32(SSH_AGENT_RSA_SHA2_512, &mut buf)?,
                        _ => write_u32(0, &mut buf)?,
                    }
                }
                Identity::Certificate(cert) => {
                    buf.write_all(&[SSH_AGENTC_SIGN_REQUEST])?;
                    let encoded_len = cert.encoded_len()?;
                    write_u32(encoded_len, &mut buf)?;
                    cert.encode(&mut buf)?;
                    write_u32(data.len(), &mut buf)?;
                    buf.write_all(data)?;
                    write_u32(0, &mut buf)?;
                }
            }
        }
    }

    write_u32(buf.len(), output)?;
    output.write_all(&buf)?;
    Ok(())
}

fn write_u32(i: usize, output: &mut dyn Write) -> Result<()> {
    let i = u32::try_from(i)
        .map_err(|_| Error::InvalidMessage(format!("Could not encode {i} into an u32 value")))?;
    output.write_all(&i.to_be_bytes())?;
    Ok(())
}

fn read_packet(mut input: impl Read) -> Result<(MessageTypeId, Bytes)> {
    let mut buf = [0u8; 5];
    match input.read_exact(&mut buf) {
        Ok(()) => {}
        Err(e) if e.kind() == ErrorKind::UnexpectedEof => {
            return invalid_data("message is too short");
        }
        Err(e) => return Err(e.into()),
    }
    let mut buf = buf.as_ref();
    let len = buf.get_length()?;
    let message_type = buf.get_u8();

    if len > MAX_MESSAGE_SIZE {
        // refusing to allocate more than MAX_MESSAGE_SIZE
        return invalid_data(&format!(
            "Refusing to read message with size larger than {MAX_MESSAGE_SIZE}"
        ));
    }
    if len < 1 {
        return invalid_data("user supplied message length is too short");
    }
    let mut bytes: BytesMut = BytesMut::zeroed(len - 1);
    input.read_exact(bytes.as_mut())?;
    Ok((message_type, bytes.freeze()))
}

fn invalid_data<T>(message: &str) -> Result<T> {
    Err(Error::InvalidMessage(String::from(message)))
}

fn make_identities<'a>(mut buf: Bytes) -> Result<Vec<Identity<'a>>> {
    let len = buf.get_length()?;
    if len > MAX_IDENTITY_COUNT {
        return invalid_data("too many identities");
    }
    let mut result: Vec<Identity> = Vec::with_capacity(len);
    for _ in 0..len {
        let key_len = buf.get_length()?;
        if key_len > buf.len() {
            return invalid_data("buffer too short");
        }
        let key_bytes = &buf.chunk()[..key_len];
        if get_key_type(key_bytes)?.contains("-cert-") {
            let cert = Certificate::from_bytes(key_bytes)?;
            buf.advance(key_len);
            // There is no setter for adding the comment to the certificate after
            // it has been created, so we have to encode it again.
            // This is not ideal, but it is the way it is for now.
            let encoded_cert = format!("{} {}", cert.to_openssh()?, get_comment(&mut buf)?);
            let cert_with_comment = Certificate::from_openssh(&encoded_cert)?;
            result.push(cert_with_comment.into());
        } else {
            let mut public_key = PublicKey::from_bytes(&buf.chunk()[..key_len])?;
            buf.advance(key_len);
            public_key.set_comment(get_comment(&mut buf)?);
            result.push(public_key.into());
        }
    }
    Ok(result)
}

fn get_comment(buf: &mut Bytes) -> Result<String> {
    let comment_len = buf.get_length()?;
    if comment_len > buf.len() {
        return invalid_data("invalid comment length");
    }
    let result = match std::str::from_utf8(&buf.chunk()[..comment_len]) {
        Ok(comment) => Ok(comment.to_string()),
        Err(_) => return invalid_data("Invalid utf-8 sequence in comment"),
    };
    buf.advance(comment_len);
    result
}

fn get_key_type(bytes: &[u8]) -> Result<String> {
    let mut buf = bytes;
    let len = buf.get_length()?;
    if buf.len() < len {
        return invalid_data("buffer too short");
    }
    String::from_utf8(buf[..len].to_vec())
        .map_err(|e| Error::InvalidMessage(format!("Invalid key type: {e}")))
}

// There are a few instances where we read an u32 from a buffer or slice and want the value as
// an usize. Let's have a single fallible implementation.
trait GetLength {
    fn get_length(&mut self) -> Result<usize>;
}

macro_rules! get_length {
    ($t:ty) => {
        impl GetLength for $t {
            fn get_length(&mut self) -> Result<usize> {
                if self.len() < 4 {
                    return invalid_data("length field is too short");
                }
                Ok(self.get_u32() as usize)
            }
        }
    };
}

get_length!(Bytes);
get_length!(&[u8]);

#[cfg(test)]
mod test {
    use crate::Error::InvalidMessage;
    use crate::codec::{
        ReadMessage, WriteMessage, get_key_type, make_identities, read_message, write_message,
        write_u32,
    };
    use crate::{Error, Identity};
    use bytes::Bytes;
    use ssh_encoding::Encode;
    use ssh_key::{Certificate, PrivateKey, PublicKey};
    use std::io::Cursor;

    pub fn reader(data: &'static [u8]) -> Cursor<&'static [u8]> {
        Cursor::new(data)
    }

    #[test]
    fn test_read_message_identities_answer() {
        let mut cursor = reader(b"\0\0\0\x05\x0c\0\0\0\0");
        let result = read_message(&mut cursor).expect("failed to read_message()");
        match result {
            ReadMessage::Identities(identities) => {
                assert_eq!(identities, vec![])
            }
            _ => panic!("result was not IdentitiesAnswer"),
        }
    }

    #[test]
    fn test_invalid_message() {
        // this message is too short, but long enough for the first read to succeed
        let mut cursor = reader(b"\0\0\0\0\x0d");
        let result = read_message(&mut cursor);
        match result {
            Err(Error::InvalidMessage(_)) => (),
            _ => panic!("did not receive expected error InvalidData"),
        }
        // this message is just too short
        let mut cursor = reader(b"\0\0\0\0");
        let result = read_message(&mut cursor);
        match result {
            Err(Error::InvalidMessage(_)) => (),
            _ => panic!("did not receive expected error InvalidData"),
        }
    }

    #[test]
    fn test_read_message_failure() {
        let mut cursor = reader(b"\0\0\0\x01\x05");
        let result = read_message(&mut cursor).expect("failed to read_message()");
        match result {
            ReadMessage::Failure => (),
            _ => panic!("result was not FailureAnswer"),
        }
    }

    #[test]
    fn test_read_message_success() {
        let mut cursor = reader(b"\0\0\0\x01\x06");
        let result = read_message(&mut cursor).expect("failed to read_message()");
        match result {
            ReadMessage::Success => (),
            _ => panic!("result was not SuccessAnswer"),
        }
    }

    #[test]
    fn test_read_message_unknown() {
        let mut cursor = reader(b"\0\0\0\x01\xff");
        let result = read_message(&mut cursor);
        match result {
            Err(Error::UnknownMessageType(_)) => (),
            _ => panic!("did not receive expected error UnknownMessageType"),
        }
    }

    #[test]
    fn test_read_overly_long_message_length() {
        let mut cursor = reader(b"\x01\0\0\x01\xff");
        let result = read_message(&mut cursor);
        match result {
            Err(InvalidMessage(msg)) => assert_eq!(
                msg,
                "Refusing to read message with size larger than 1048576"
            ),
            _ => panic!("did not receive expected error InvalidData"),
        }
    }

    #[test]
    fn test_make_identities() {
        let data = Bytes::from_static(include_bytes!(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/tests/data/identity_list_response.bin"
        )));
        let key = include_str!(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/tests/data/id_ed25519.pub"
        ));
        let identity: Identity = PublicKey::from_openssh(key).unwrap().into();

        assert_eq!(
            make_identities(data).expect("Could not decode"),
            vec![identity]
        )
    }

    macro_rules! read_str {
        ($s:expr) => {
            include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/tests/data/", $s))
        };
    }

    // If certificates are present, we handle them too from the ssh-agent
    #[test]
    fn test_make_identities_with_cert() -> Result<(), Error> {
        // this file contains a regular public key and a cert, then a key at the end
        let data = Bytes::from_static(include_bytes!(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/tests/data/identities_with_cert.bin"
        )));
        let identities = make_identities(data)?;
        assert_eq!(3, identities.len());

        let mut identities = identities.iter();
        if let Identity::PublicKey(pk) = identities.next().unwrap() {
            compare_to_key(read_str!("id_ed25519_for_cert.pub"), pk);
        } else {
            panic!("did not receive expected public key");
        }

        if let Identity::Certificate(cert) = identities.next().unwrap() {
            compare_to_cert(read_str!("id_ed25519_for_cert-cert.pub"), cert);
        } else {
            panic!("did not receive expected cert");
        }

        if let Identity::PublicKey(pk) = identities.next().unwrap() {
            compare_to_key(read_str!("id_ecdsa.pub"), pk);
        } else {
            panic!("did not receive expected public key");
        }
        Ok(())
    }

    fn compare_to_key(expected: &str, actual: &PublicKey) {
        assert_eq!(
            PublicKey::from_openssh(expected).unwrap().key_data(),
            actual.key_data()
        )
    }

    fn compare_to_cert(expected: &str, actual: &Certificate) {
        assert_eq!(
            Certificate::from_openssh(expected).unwrap().public_key(),
            actual.public_key()
        )
    }

    #[test]
    fn test_make_identities_malicious_data() {
        // Make sure we are not allocating for a list of 2**32 identities
        let bytes = Bytes::from_static(b"\xff\xff\xff\xff");
        let result = make_identities(bytes);
        match result {
            Err(InvalidMessage(_)) => (),
            _ => panic!("did not receive expected error InvalidData"),
        }

        // Make sure that we don't panic if the key length specified to be longer than the remaining buffer
        let bytes = Bytes::from_static(b"\0\0\0\x01\0\0\0\x25");
        let result = make_identities(bytes);
        match result {
            Err(InvalidMessage(_)) => (),
            _ => panic!("did not receive expected error InvalidData"),
        }

        // Make sure that we don't panic if the comment length is specified to be longer than the remaining buffer
        let key = PublicKey::from_openssh(read_str!("id_ed25519.pub")).unwrap();
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&1_u32.to_be_bytes());
        bytes.extend_from_slice(&(key.key_data().encoded_len().unwrap() as u32).to_be_bytes());
        key.key_data().encode(&mut bytes).unwrap();
        bytes.extend_from_slice(&1_u32.to_be_bytes());
        let result = make_identities(bytes.into());
        match result {
            Err(InvalidMessage(_)) => (),
            _ => panic!("did not receive expected error InvalidData"),
        }
    }

    #[test]
    fn test_write_message() {
        let mut output: Vec<u8> = Vec::new();
        write_message(&mut output, WriteMessage::RequestIdentities).expect("failed writing");
        assert_eq!(vec![0_u8, 0, 0, 1, 11], output)
    }

    macro_rules! add_identity {
        ($message_path:expr, $key_path:expr) => {
            let key = include_str!(concat!(
                env!("CARGO_MANIFEST_DIR"),
                "/tests/data/",
                $key_path
            ));
            let expected = include_bytes!(concat!(
                env!("CARGO_MANIFEST_DIR"),
                "/tests/data/",
                $message_path
            ));
            let mut output: Vec<u8> = Vec::new();
            let key = PrivateKey::from_openssh(key).expect("failed to parse key");
            write_message(&mut output, WriteMessage::AddIdentity(&key)).unwrap();
            assert_eq!(expected, output.as_slice());
        };
    }

    #[test]
    fn test_write_add_identity() {
        add_identity!("ssh-add_rsa.bin", "id_rsa");
        add_identity!("ssh-add_dsa.bin", "id_dsa");
        add_identity!("ssh-add_ed25519.bin", "id_ed25519");
        add_identity!("ssh-add_ecdsa.bin", "id_ecdsa");
    }

    macro_rules! remove_identity {
        ($message_path:expr, $key_path:expr) => {
            let key = include_str!(concat!(
                env!("CARGO_MANIFEST_DIR"),
                "/tests/data/",
                $key_path
            ));
            let expected = include_bytes!(concat!(
                env!("CARGO_MANIFEST_DIR"),
                "/tests/data/",
                $message_path
            ));
            let mut output: Vec<u8> = Vec::new();
            let key = PrivateKey::from_openssh(key).expect("failed to parse key");
            write_message(&mut output, WriteMessage::RemoveIdentity(&key)).unwrap();
            assert_eq!(expected, output.as_slice());
        };
    }

    #[test]
    fn test_write_remove_identity() {
        remove_identity!("ssh-remove_rsa.bin", "id_rsa");
        remove_identity!("ssh-remove_dsa.bin", "id_dsa");
        remove_identity!("ssh-remove_ed25519.bin", "id_ed25519");
        remove_identity!("ssh-remove_ecdsa.bin", "id_ecdsa");
    }

    #[test]
    fn test_write_remove_all_identities() {
        let mut output: Vec<u8> = Vec::new();
        write_message(&mut output, WriteMessage::RemoveAllIdentities).expect("failed writing");
        assert_eq!(vec![0_u8, 0, 0, 1, 19], output)
    }

    #[test]
    // On 32-bit platforms, usize is 32 bits, so usize::MAX fits in a u32 and the test fails.
    #[cfg(target_pointer_width = "64")]
    fn test_write_too_large() {
        let mut output: Vec<u8> = Vec::new();
        let result = write_u32(usize::MAX, &mut output);
        match result {
            Err(InvalidMessage(msg)) => {
                assert_eq!(
                    format!("Could not encode {} into an u32 value", usize::MAX),
                    msg
                )
            }
            _ => panic!("expected InvalidMessage"),
        }
    }

    // let's verify that we set the correct signature flag, SSH_AGENT_RSA_SHA2_512
    #[test]
    fn test_write_sign_rsa() {
        let key = include_str!(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/tests/data/id_rsa.pub",
        ));
        let expected = include_bytes!(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/tests/data/sign_rsa.bin",
        ));

        let key = PublicKey::from_openssh(key).expect("failed to parse key");

        let mut output: Vec<u8> = Vec::new();
        write_message(&mut output, WriteMessage::Sign(&key.into(), b"a")).unwrap();
        assert_eq!(expected, output.as_slice());
    }

    #[test]
    fn test_get_key_type() -> Result<(), Error> {
        // exact length
        let buf = b"\0\0\0\x03foo";
        assert_eq!(get_key_type(buf)?, "foo");

        // some extra bytes is fine
        let buf = b"\0\0\0\x03foobar";
        assert_eq!(get_key_type(buf)?, "foo");

        // not being able to read length not okay
        let buf = b"\0\0\0";
        match get_key_type(buf).unwrap_err() {
            InvalidMessage(msg) => {
                assert_eq!("length field is too short", msg)
            }
            _ => panic!("expected InvalidMessage"),
        }

        let buf = b"\0\0\0\x03f";
        match get_key_type(buf).unwrap_err() {
            InvalidMessage(msg) => {
                assert_eq!("buffer too short", msg)
            }
            _ => panic!("expected InvalidMessage"),
        }

        // invalid utf-8 sequence
        let buf = b"\0\0\0\x03f\xc0\xaf";
        match get_key_type(buf).unwrap_err() {
            InvalidMessage(msg) => {
                assert_eq!(
                    "Invalid key type: invalid utf-8 sequence of 1 bytes from index 1",
                    msg
                )
            }
            _ => panic!("expected InvalidMessage"),
        }

        Ok(())
    }
}