Creating postgres schemas using psycopg cur.execute - postgresql

Question

My python application allows users to create schemas of their naming. I need a way to protect the application from sql injections.
The SQL to be executed reads
CREATE SCHEMA schema_name AUTHORIZATION user_name;
The psycopg documentation (generally) recommends passing parameters to execute like so
conn = psycopg2.connect("dbname=test user=postgres")
cur = conn.cursor()
query = 'CREATE SCHEMA IF NOT EXISTS %s AUTHORIZATION %s;'
params = ('schema_name', 'user_name')
cur.execute(query, params)
But this results in a query with single quotes, which fails:
CREATE SCHEMA 'schema_name' AUTHORIZATION 'user_name';
> fail
Is there a way to remove the quotes, or should I just settle for stripping non-alphanumeric characters from the schema name and call it a day? The later seems kind of ugly, but should still work.

Answer 1

To pass identifiers use AsIs. But that exposes to SQL injection:
import psycopg2
from psycopg2.extensions import AsIs
conn = psycopg2.connect(database='cpn')
cursor = conn.cursor()
query = """CREATE SCHEMA %s AUTHORIZATION %s;"""
param = (AsIs('u1'), AsIs('u1; select * from user_table'))
print cursor.mogrify(query, param)
Output:
CREATE SCHEMA u1 AUTHORIZATION u1; select * from user_table;

Answer 2

Here's a boilerplate that might help. I've used environment variables but you can use a .conf or whatever you like.
Store your connection variables in a .env file:
db_host = "localhost"
db_port = "5432"
db_database = "postgres"
db_user = "postgres"
db_password = "postgres"
db_schema = "schema2"
Load params in your app.py and assign them to variables, then use the variables where required:
import psychopg2
from dotenv import load_dotenv
import database
# Load your environment variables here:
load_dotenv()
db_host = os.environ["db_host"]
db_port = os.environ["db_port"]
db_database = os.environ["db_database"]
db_user = os.environ["db_user"]
db_password = os.environ["db_password"]
db_schema = os.environ["db_schema"]
# Build Connection:
connection = psycopg2.connect(host=db_host,
port=db_port,
database=db_database,
user=db_user,
password=db_password
)
# Build Query Strings:
CREATE_SCHEMA = f"CREATE SCHEMA IF NOT EXISTS {schema};"
CREATE_TABLE1 = f"CREATE TABLE IF NOT EXISTS {schema}.table1 (...);"
CREATE_TABLE2 = f"CREATE TABLE IF NOT EXISTS {schema}.table2 (...);"
# Create Schema and Tables:
with connection:
with connection.cursor() as cursor:
cursor.execute(CREATE_SCHEMA)
cursor.execute(CREATE_TABLE1)
cursor.execute(CREATE_TABLE2)

Answer 3

As of psycopg2 >= 2.7, psycopg2.sql can be used to compose dynamic statements, which also guards from SQL injection.