static int ssl_parse_client_key_exchange( mbedtls_ssl_context *ssl )
{
    int ret;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
    unsigned char *p, *end;

    ciphersuite_info = ssl->transform_negotiate->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client key exchange" ) );

    if( ( ret = mbedtls_ssl_read_record( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
        return( ret );
    }

    p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
    end = ssl->in_msg + ssl->in_hslen;

    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

    if( ssl->in_msg[0] != MBEDTLS_SSL_HS_CLIENT_KEY_EXCHANGE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA )
    {
        if( ( ret = ssl_parse_client_dh_public( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_dh_public" ), ret );
            return( ret );
        }

        if( p != end )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
        }

        if( ( ret = mbedtls_dhm_calc_secret( &ssl->handshake->dhm_ctx,
                                      ssl->handshake->premaster,
                                      MBEDTLS_PREMASTER_SIZE,
                                     &ssl->handshake->pmslen,
                                      ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_calc_secret", ret );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS );
        }

        MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||                   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||                      \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA )
    {
        if( ( ret = mbedtls_ecdh_read_public( &ssl->handshake->ecdh_ctx,
                                      p, end - p) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_read_public", ret );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
        }

        MBEDTLS_SSL_DEBUG_ECP( 3, "ECDH: Qp ", &ssl->handshake->ecdh_ctx.Qp );

        if( ( ret = mbedtls_ecdh_calc_secret( &ssl->handshake->ecdh_ctx,
                                      &ssl->handshake->pmslen,
                                       ssl->handshake->premaster,
                                       MBEDTLS_MPI_MAX_SIZE,
                                       ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_calc_secret", ret );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS );
        }

        MBEDTLS_SSL_DEBUG_MPI( 3, "ECDH: z  ", &ssl->handshake->ecdh_ctx.z );
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK )
    {
        if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
            return( ret );
        }

        if( p != end )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
        }

        if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                        ciphersuite_info->key_exchange ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
    {
        if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
            return( ret );
        }

        if( ( ret = ssl_parse_encrypted_pms( ssl, p, end, 2 ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_encrypted_pms" ), ret );
            return( ret );
        }

        if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                        ciphersuite_info->key_exchange ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK )
    {
        if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
            return( ret );
        }
        if( ( ret = ssl_parse_client_dh_public( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_dh_public" ), ret );
            return( ret );
        }

        if( p != end )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
        }

        if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                        ciphersuite_info->key_exchange ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK )
    {
        if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
            return( ret );
        }

        if( ( ret = mbedtls_ecdh_read_public( &ssl->handshake->ecdh_ctx,
                                       p, end - p ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_read_public", ret );
            return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
        }

        MBEDTLS_SSL_DEBUG_ECP( 3, "ECDH: Qp ", &ssl->handshake->ecdh_ctx.Qp );

        if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                        ciphersuite_info->key_exchange ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA )
    {
        if( ( ret = ssl_parse_encrypted_pms( ssl, p, end, 0 ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_parse_encrypted_pms_secret" ), ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE )
    {
        ret = mbedtls_ecjpake_read_round_two( &ssl->handshake->ecjpake_ctx,
                                              p, end - p );
        if( ret != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_read_round_two", ret );
            return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
        }

        ret = mbedtls_ecjpake_derive_secret( &ssl->handshake->ecjpake_ctx,
                ssl->handshake->premaster, 32, &ssl->handshake->pmslen,
                ssl->conf->f_rng, ssl->conf->p_rng );
        if( ret != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_derive_secret", ret );
            return( ret );
        }
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    if( ( ret = mbedtls_ssl_derive_keys( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_derive_keys", ret );
        return( ret );
    }

    ssl->state++;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client key exchange" ) );

    return( 0 );
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.