rustls/server/

hs.rs

use crate::common_state::State;
use crate::conn::ConnectionRandoms;
#[cfg(feature = "tls12")]
use crate::enums::CipherSuite;
use crate::enums::{AlertDescription, HandshakeType, ProtocolVersion, SignatureScheme};
use crate::error::{Error, PeerIncompatible, PeerMisbehaved};
use crate::hash_hs::{HandshakeHash, HandshakeHashBuffer};
#[cfg(feature = "logging")]
use crate::log::{debug, trace};
use crate::msgs::enums::{Compression, ExtensionType};
#[cfg(feature = "tls12")]
use crate::msgs::handshake::SessionId;
use crate::msgs::handshake::{ClientHelloPayload, Random, ServerExtension};
use crate::msgs::handshake::{ConvertProtocolNameList, ConvertServerNameList, HandshakePayload};
use crate::msgs::message::{Message, MessagePayload};
use crate::msgs::persist;
use crate::server::{ClientHello, ServerConfig};
use crate::suites;
use crate::SupportedCipherSuite;

use super::server_conn::ServerConnectionData;
#[cfg(feature = "tls12")]
use super::tls12;
use crate::server::common::ActiveCertifiedKey;
use crate::server::tls13;

use pki_types::DnsName;

use alloc::borrow::ToOwned;
use alloc::boxed::Box;
use alloc::sync::Arc;
use alloc::vec::Vec;

pub(super) type NextState = Box<dyn State<ServerConnectionData>>;
pub(super) type NextStateOrError = Result<NextState, Error>;
pub(super) type ServerContext<'a> = crate::common_state::Context<'a, ServerConnectionData>;

pub(super) fn can_resume(
    suite: SupportedCipherSuite,
    sni: &Option<DnsName>,
    using_ems: bool,
    resumedata: &persist::ServerSessionValue,
) -> bool {
    // The RFCs underspecify what happens if we try to resume to
    // an unoffered/varying suite.  We merely don't resume in weird cases.
    //
    // RFC 6066 says "A server that implements this extension MUST NOT accept
    // the request to resume the session if the server_name extension contains
    // a different name. Instead, it proceeds with a full handshake to
    // establish a new session."
    resumedata.cipher_suite == suite.suite()
        && (resumedata.extended_ms == using_ems || (resumedata.extended_ms && !using_ems))
        && &resumedata.sni == sni
}

#[derive(Default)]
pub(super) struct ExtensionProcessing {
    // extensions to reply with
    pub(super) exts: Vec<ServerExtension>,
    #[cfg(feature = "tls12")]
    pub(super) send_ticket: bool,
}

impl ExtensionProcessing {
    pub(super) fn new() -> Self {
        Default::default()
    }

    pub(super) fn process_common(
        &mut self,
        config: &ServerConfig,
        cx: &mut ServerContext<'_>,
        ocsp_response: &mut Option<&[u8]>,
        hello: &ClientHelloPayload,
        resumedata: Option<&persist::ServerSessionValue>,
        extra_exts: Vec<ServerExtension>,
    ) -> Result<(), Error> {
        // ALPN
        let our_protocols = &config.alpn_protocols;
        let maybe_their_protocols = hello.get_alpn_extension();
        if let Some(their_protocols) = maybe_their_protocols {
            let their_protocols = their_protocols.to_slices();

            if their_protocols
                .iter()
                .any(|protocol| protocol.is_empty())
            {
                return Err(PeerMisbehaved::OfferedEmptyApplicationProtocol.into());
            }

            cx.common.alpn_protocol = our_protocols
                .iter()
                .find(|protocol| their_protocols.contains(&protocol.as_slice()))
                .cloned();
            if let Some(ref selected_protocol) = cx.common.alpn_protocol {
                debug!("Chosen ALPN protocol {:?}", selected_protocol);
                self.exts
                    .push(ServerExtension::make_alpn(&[selected_protocol]));
            } else if !our_protocols.is_empty() {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::NoApplicationProtocol,
                    Error::NoApplicationProtocol,
                ));
            }
        }

        if cx.common.is_quic() {
            // QUIC has strict ALPN, unlike TLS's more backwards-compatible behavior. RFC 9001
            // says: "The server MUST treat the inability to select a compatible application
            // protocol as a connection error of type 0x0178". We judge that ALPN was desired
            // (rather than some out-of-band protocol negotiation mechanism) iff any ALPN
            // protocols were configured locally or offered by the client. This helps prevent
            // successful establishment of connections between peers that can't understand
            // each other.
            if cx.common.alpn_protocol.is_none()
                && (!our_protocols.is_empty() || maybe_their_protocols.is_some())
            {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::NoApplicationProtocol,
                    Error::NoApplicationProtocol,
                ));
            }

            match hello.get_quic_params_extension() {
                Some(params) => cx.common.quic.params = Some(params),
                None => {
                    return Err(cx
                        .common
                        .missing_extension(PeerMisbehaved::MissingQuicTransportParameters));
                }
            }
        }

        let for_resume = resumedata.is_some();
        // SNI
        if !for_resume && hello.get_sni_extension().is_some() {
            self.exts
                .push(ServerExtension::ServerNameAck);
        }

        // Send status_request response if we have one.  This is not allowed
        // if we're resuming, and is only triggered if we have an OCSP response
        // to send.
        if !for_resume
            && hello
                .find_extension(ExtensionType::StatusRequest)
                .is_some()
        {
            if ocsp_response.is_some() && !cx.common.is_tls13() {
                // Only TLS1.2 sends confirmation in ServerHello
                self.exts
                    .push(ServerExtension::CertificateStatusAck);
            }
        } else {
            // Throw away any OCSP response so we don't try to send it later.
            ocsp_response.take();
        }

        self.exts.extend(extra_exts);

        Ok(())
    }

    #[cfg(feature = "tls12")]
    pub(super) fn process_tls12(
        &mut self,
        config: &ServerConfig,
        hello: &ClientHelloPayload,
        using_ems: bool,
    ) {
        // Renegotiation.
        // (We don't do reneg at all, but would support the secure version if we did.)
        let secure_reneg_offered = hello
            .find_extension(ExtensionType::RenegotiationInfo)
            .is_some()
            || hello
                .cipher_suites
                .contains(&CipherSuite::TLS_EMPTY_RENEGOTIATION_INFO_SCSV);

        if secure_reneg_offered {
            self.exts
                .push(ServerExtension::make_empty_renegotiation_info());
        }

        // Tickets:
        // If we get any SessionTicket extension and have tickets enabled,
        // we send an ack.
        if hello
            .find_extension(ExtensionType::SessionTicket)
            .is_some()
            && config.ticketer.enabled()
        {
            self.send_ticket = true;
            self.exts
                .push(ServerExtension::SessionTicketAck);
        }

        // Confirm use of EMS if offered.
        if using_ems {
            self.exts
                .push(ServerExtension::ExtendedMasterSecretAck);
        }
    }
}

pub(super) struct ExpectClientHello {
    pub(super) config: Arc<ServerConfig>,
    pub(super) extra_exts: Vec<ServerExtension>,
    pub(super) transcript: HandshakeHashOrBuffer,
    #[cfg(feature = "tls12")]
    pub(super) session_id: SessionId,
    #[cfg(feature = "tls12")]
    pub(super) using_ems: bool,
    pub(super) done_retry: bool,
    pub(super) send_tickets: usize,
}

impl ExpectClientHello {
    pub(super) fn new(config: Arc<ServerConfig>, extra_exts: Vec<ServerExtension>) -> Self {
        let mut transcript_buffer = HandshakeHashBuffer::new();

        if config.verifier.offer_client_auth() {
            transcript_buffer.set_client_auth_enabled();
        }

        Self {
            config,
            extra_exts,
            transcript: HandshakeHashOrBuffer::Buffer(transcript_buffer),
            #[cfg(feature = "tls12")]
            session_id: SessionId::empty(),
            #[cfg(feature = "tls12")]
            using_ems: false,
            done_retry: false,
            send_tickets: 0,
        }
    }

    /// Continues handling of a `ClientHello` message once config and certificate are available.
    pub(super) fn with_certified_key(
        self,
        mut sig_schemes: Vec<SignatureScheme>,
        client_hello: &ClientHelloPayload,
        m: &Message,
        cx: &mut ServerContext<'_>,
    ) -> NextStateOrError {
        let tls13_enabled = self
            .config
            .supports_version(ProtocolVersion::TLSv1_3);
        let tls12_enabled = self
            .config
            .supports_version(ProtocolVersion::TLSv1_2);

        // Are we doing TLS1.3?
        let maybe_versions_ext = client_hello.get_versions_extension();
        let version = if let Some(versions) = maybe_versions_ext {
            if versions.contains(&ProtocolVersion::TLSv1_3) && tls13_enabled {
                ProtocolVersion::TLSv1_3
            } else if !versions.contains(&ProtocolVersion::TLSv1_2) || !tls12_enabled {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::ProtocolVersion,
                    PeerIncompatible::Tls12NotOfferedOrEnabled,
                ));
            } else if cx.common.is_quic() {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::ProtocolVersion,
                    PeerIncompatible::Tls13RequiredForQuic,
                ));
            } else {
                ProtocolVersion::TLSv1_2
            }
        } else if client_hello.client_version.get_u16() < ProtocolVersion::TLSv1_2.get_u16() {
            return Err(cx.common.send_fatal_alert(
                AlertDescription::ProtocolVersion,
                PeerIncompatible::Tls12NotOffered,
            ));
        } else if !tls12_enabled && tls13_enabled {
            return Err(cx.common.send_fatal_alert(
                AlertDescription::ProtocolVersion,
                PeerIncompatible::SupportedVersionsExtensionRequired,
            ));
        } else if cx.common.is_quic() {
            return Err(cx.common.send_fatal_alert(
                AlertDescription::ProtocolVersion,
                PeerIncompatible::Tls13RequiredForQuic,
            ));
        } else {
            ProtocolVersion::TLSv1_2
        };

        cx.common.negotiated_version = Some(version);

        // We communicate to the upper layer what kind of key they should choose
        // via the sigschemes value.  Clients tend to treat this extension
        // orthogonally to offered ciphersuites (even though, in TLS1.2 it is not).
        // So: reduce the offered sigschemes to those compatible with the
        // intersection of ciphersuites.
        let client_suites = self
            .config
            .provider
            .cipher_suites
            .iter()
            .copied()
            .filter(|scs| {
                client_hello
                    .cipher_suites
                    .contains(&scs.suite())
            })
            .collect::<Vec<_>>();

        sig_schemes
            .retain(|scheme| suites::compatible_sigscheme_for_suites(*scheme, &client_suites));

        // Choose a certificate.
        let certkey = {
            let client_hello = ClientHello::new(
                &cx.data.sni,
                &sig_schemes,
                client_hello.get_alpn_extension(),
                &client_hello.cipher_suites,
            );

            let certkey = self
                .config
                .cert_resolver
                .resolve(client_hello);

            certkey.ok_or_else(|| {
                cx.common.send_fatal_alert(
                    AlertDescription::AccessDenied,
                    Error::General("no server certificate chain resolved".to_owned()),
                )
            })?
        };
        let certkey = ActiveCertifiedKey::from_certified_key(&certkey);

        // Reduce our supported ciphersuites by the certificate.
        // (no-op for TLS1.3)
        let suitable_suites = suites::reduce_given_sigalg(
            &self.config.provider.cipher_suites,
            certkey.get_key().algorithm(),
        );

        // And version
        let suitable_suites = suites::reduce_given_version_and_protocol(
            &suitable_suites,
            version,
            cx.common.protocol,
        );

        let suite = if self.config.ignore_client_order {
            suites::choose_ciphersuite_preferring_server(
                &client_hello.cipher_suites,
                &suitable_suites,
            )
        } else {
            suites::choose_ciphersuite_preferring_client(
                &client_hello.cipher_suites,
                &suitable_suites,
            )
        }
        .ok_or_else(|| {
            cx.common.send_fatal_alert(
                AlertDescription::HandshakeFailure,
                PeerIncompatible::NoCipherSuitesInCommon,
            )
        })?;

        debug!("decided upon suite {:?}", suite);
        cx.common.suite = Some(suite);

        // Start handshake hash.
        let starting_hash = suite.hash_provider();
        let transcript = match self.transcript {
            HandshakeHashOrBuffer::Buffer(inner) => inner.start_hash(starting_hash),
            HandshakeHashOrBuffer::Hash(inner)
                if inner.algorithm() == starting_hash.algorithm() =>
            {
                inner
            }
            _ => {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::IllegalParameter,
                    PeerMisbehaved::HandshakeHashVariedAfterRetry,
                ));
            }
        };

        // Save their Random.
        let randoms = ConnectionRandoms::new(
            client_hello.random,
            Random::new(self.config.provider.secure_random)?,
        );
        match suite {
            SupportedCipherSuite::Tls13(suite) => tls13::CompleteClientHelloHandling {
                config: self.config,
                transcript,
                suite,
                randoms,
                done_retry: self.done_retry,
                send_tickets: self.send_tickets,
                extra_exts: self.extra_exts,
            }
            .handle_client_hello(cx, certkey, m, client_hello, sig_schemes),
            #[cfg(feature = "tls12")]
            SupportedCipherSuite::Tls12(suite) => tls12::CompleteClientHelloHandling {
                config: self.config,
                transcript,
                session_id: self.session_id,
                suite,
                using_ems: self.using_ems,
                randoms,
                send_ticket: self.send_tickets > 0,
                extra_exts: self.extra_exts,
            }
            .handle_client_hello(
                cx,
                certkey,
                m,
                client_hello,
                sig_schemes,
                tls13_enabled,
            ),
        }
    }
}

impl State<ServerConnectionData> for ExpectClientHello {
    fn handle(self: Box<Self>, cx: &mut ServerContext<'_>, m: Message) -> NextStateOrError {
        let (client_hello, sig_schemes) = process_client_hello(&m, self.done_retry, cx)?;
        self.with_certified_key(sig_schemes, client_hello, &m, cx)
    }
}

/// Configuration-independent validation of a `ClientHello` message.
///
/// This represents the first part of the `ClientHello` handling, where we do all validation that
/// doesn't depend on a `ServerConfig` being available and extract everything needed to build a
/// [`ClientHello`] value for a [`ResolvesServerCert`].
///
/// Note that this will modify `data.sni` even if config or certificate resolution fail.
///
/// [`ResolvesServerCert`]: crate::server::ResolvesServerCert
pub(super) fn process_client_hello<'a>(
    m: &'a Message,
    done_retry: bool,
    cx: &mut ServerContext,
) -> Result<(&'a ClientHelloPayload, Vec<SignatureScheme>), Error> {
    let client_hello =
        require_handshake_msg!(m, HandshakeType::ClientHello, HandshakePayload::ClientHello)?;
    trace!("we got a clienthello {:?}", client_hello);

    if !client_hello
        .compression_methods
        .contains(&Compression::Null)
    {
        return Err(cx.common.send_fatal_alert(
            AlertDescription::IllegalParameter,
            PeerIncompatible::NullCompressionRequired,
        ));
    }

    if client_hello.has_duplicate_extension() {
        return Err(cx.common.send_fatal_alert(
            AlertDescription::DecodeError,
            PeerMisbehaved::DuplicateClientHelloExtensions,
        ));
    }

    // No handshake messages should follow this one in this flight.
    cx.common.check_aligned_handshake()?;

    // Extract and validate the SNI DNS name, if any, before giving it to
    // the cert resolver. In particular, if it is invalid then we should
    // send an Illegal Parameter alert instead of the Internal Error alert
    // (or whatever) that we'd send if this were checked later or in a
    // different way.
    let sni: Option<DnsName> = match client_hello.get_sni_extension() {
        Some(sni) => {
            if sni.has_duplicate_names_for_type() {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::DecodeError,
                    PeerMisbehaved::DuplicateServerNameTypes,
                ));
            }

            if let Some(hostname) = sni.get_single_hostname() {
                Some(hostname.to_lowercase_owned())
            } else {
                return Err(cx.common.send_fatal_alert(
                    AlertDescription::IllegalParameter,
                    PeerMisbehaved::ServerNameMustContainOneHostName,
                ));
            }
        }
        None => None,
    };

    // save only the first SNI
    if let (Some(sni), false) = (&sni, done_retry) {
        // Save the SNI into the session.
        // The SNI hostname is immutable once set.
        assert!(cx.data.sni.is_none());
        cx.data.sni = Some(sni.clone());
    } else if cx.data.sni != sni {
        return Err(PeerMisbehaved::ServerNameDifferedOnRetry.into());
    }

    let sig_schemes = client_hello
        .get_sigalgs_extension()
        .ok_or_else(|| {
            cx.common.send_fatal_alert(
                AlertDescription::HandshakeFailure,
                PeerIncompatible::SignatureAlgorithmsExtensionRequired,
            )
        })?;

    Ok((client_hello, sig_schemes.to_owned()))
}

#[allow(clippy::large_enum_variant)]
pub(crate) enum HandshakeHashOrBuffer {
    Buffer(HandshakeHashBuffer),
    Hash(HandshakeHash),
}