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dtls.c: Check for optional handshake messages

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In general the handshake state machine forces the handshakes to go
through a defined order. But optional handshake message are not
controlled by that.

This fix introduces a optional handshake message field. This new
field enables the state-machine to check if this message
is (optionally) expected. When processed, the field is reset and
receiving the optional message twice will therefore fail the
handshake.

Fixes: Issue #78

Signed-off-by: Achim Kraus <achim.kraus@bosch.io>
This commit is contained in:
Achim Kraus 2021-11-22 10:47:26 +01:00
parent 52f65d61ce
commit 40d863c115
3 changed files with 16 additions and 3 deletions
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13
dtls.c
View File

@ -3440,6 +3440,7 @@ dtls_renegotiate(dtls_context_t *ctx, const session_t *dst)
peer->handshake_params->hs_state.mseq_r = 0;
peer->handshake_params->hs_state.mseq_s = 0;
peer->optional_handshake_message = DTLS_HT_NO_OPTIONAL_MESSAGE;
if (peer->role == DTLS_CLIENT) {
/* send ClientHello with empty Cookie */
@ -3553,8 +3554,10 @@ handle_handshake_msg(dtls_context_t *ctx, dtls_peer_t *peer, uint8 *data, size_t
}
if (is_tls_ecdhe_ecdsa_with_aes_128_ccm_8(peer->handshake_params->cipher))
peer->state = DTLS_STATE_WAIT_SERVERCERTIFICATE;
else
else {
peer->optional_handshake_message = DTLS_HT_SERVER_KEY_EXCHANGE;
peer->state = DTLS_STATE_WAIT_SERVERHELLODONE;
}
/* update_hs_hash(peer, data, data_length); */
break;
@ -3588,14 +3591,16 @@ handle_handshake_msg(dtls_context_t *ctx, dtls_peer_t *peer, uint8 *data, size_t
if (state != DTLS_STATE_WAIT_SERVERKEYEXCHANGE) {
return dtls_alert_fatal_create(DTLS_ALERT_UNEXPECTED_MESSAGE);
}
peer->optional_handshake_message = DTLS_HT_CERTIFICATE_REQUEST;
err = check_server_key_exchange_ecdsa(ctx, peer, data, data_length);
}
#endif /* DTLS_ECC */
#ifdef DTLS_PSK
if (is_tls_psk_with_aes_128_ccm_8(peer->handshake_params->cipher)) {
if (state != DTLS_STATE_WAIT_SERVERHELLODONE) {
if (state != DTLS_STATE_WAIT_SERVERHELLODONE || peer->optional_handshake_message != DTLS_HT_SERVER_KEY_EXCHANGE) {
return dtls_alert_fatal_create(DTLS_ALERT_UNEXPECTED_MESSAGE);
}
peer->optional_handshake_message = DTLS_HT_NO_OPTIONAL_MESSAGE;
err = check_server_key_exchange_psk(ctx, peer, data, data_length);
}
#endif /* DTLS_PSK */
@ -3629,10 +3634,11 @@ handle_handshake_msg(dtls_context_t *ctx, dtls_peer_t *peer, uint8 *data, size_t
case DTLS_HT_CERTIFICATE_REQUEST:
if (state != DTLS_STATE_WAIT_SERVERHELLODONE ||
peer->optional_handshake_message != DTLS_HT_CERTIFICATE_REQUEST ||
!is_tls_ecdhe_ecdsa_with_aes_128_ccm_8(peer->handshake_params->cipher)) {
return dtls_alert_fatal_create(DTLS_ALERT_UNEXPECTED_MESSAGE);
}
peer->optional_handshake_message = DTLS_HT_NO_OPTIONAL_MESSAGE;
err = check_certificate_request(ctx, peer, data, data_length);
if (err < 0) {
dtls_warn("error in check_certificate_request err: %i\n", err);
@ -3785,6 +3791,7 @@ handle_handshake_msg(dtls_context_t *ctx, dtls_peer_t *peer, uint8 *data, size_t
return err;
}
peer->state = DTLS_STATE_CLIENTHELLO;
peer->optional_handshake_message = DTLS_HT_NO_OPTIONAL_MESSAGE;
break;
default:

5
dtls.h
View File

@ -348,6 +348,11 @@ typedef struct __attribute__((__packed__)) {
#define DTLS_HT_CLIENT_KEY_EXCHANGE 16
#define DTLS_HT_FINISHED 20
/**
* Pseudo handshake message type, if no optional handshake message is expected.
*/
#define DTLS_HT_NO_OPTIONAL_MESSAGE -1
/** Header structure for the DTLS handshake protocol. */
typedef struct __attribute__((__packed__)) {
uint8 msg_type; /**< Type of handshake message (one of DTLS_HT_) */

1
peer.h
View File

@ -52,6 +52,7 @@ typedef struct dtls_peer_t {
dtls_peer_type role; /**< denotes if this host is DTLS_CLIENT or DTLS_SERVER */
dtls_state_t state; /**< DTLS engine state */
int16_t optional_handshake_message; /**< optional next handshake message, DTLS_HT_NO_OPTIONAL_MESSAGE, if no optional message is expected. */
dtls_security_parameters_t *security_params[2];
dtls_handshake_parameters_t *handshake_params;