sql_firewall is a PostgreSQL extension which is intended to protect database from SQL injections or unexpected queries.
sql_firewall module learns queries which can be executed, and prevents/warns on executing queries which are not found in the learned firewall rule.
sql_firewall can take one of four modes specified in sql_firewall.firewall parameter: "learning", "enforcing", "permissive" and "disabled".
In the "learning" mode, sql_firewall collects pairs of "userid" and "queryid" associated with the executed queries. "queryid" is calculated based on a parse tree, similar to pg_stat_statements.
In the "enforcing" mode, sql_firewall checks whether queries are in the list of collected pairs of "userid" and "queryid", the firewall rules. When a query not in the firewall rules comes in, sql_firewall produces an error with the message to prevent execution.
In the "permissive" mode, sql_firewall checks queries as well, but allows to execute even not in the firewall rules. And produces warnings if the queries are not in the rules.
sql_firewall supports PostgreSQL 9.4.x. Other major versions would be supported in the future release.
Exported rule files would not be compatible between different PostgreSQL major versions, because queryid is calculated from the internal data structure (the Query structure) which is different in different major versions.
sql_firewall can be built as a PostgreSQL extension.
$ export PATH=$PGHOME/bin:$PATH
$ export USE_PGXS=1
$ make
$ sudo make install $ vi $PGDATA/postgresql.conf
<add>
shared_preload_libraries = 'sql_firewall'
sql_firewall.firewall = 'learning'
</add>
$ pg_ctl -D $PGDATA restart
$ psql mydb
mydb=# create extension sql_firewall;sql_firewall would check all queries incoming to not only the specific database where the module is installed, but all the databases in the entire PostgreSQL cluster.
Even though, the views and functions in the module would be available only on the installed database.
shared_preload_libraries
sql_firewall module needs to be loaded in the shared_preload_libraries parameter as following:
shared_preload_libraries = 'sql_firewall'
pg_stat_statements built with `--enable-cassert' causes assert when queryId already has non-zero value.
So, to use both pg_stat_statements and sql_firewall at the same time, pg_stat_statements needs to be loaded prior to sql_firewall in the shared_preload_libraries parameter as following.
shared_preload_libraries = 'pg_stat_statements,sql_firewall'
Then, sql_firewall can skip queryId calculation if queryId is already set by pg_stat_statements, and avoid the assert.
sql_firewall.firewall
sql_firewall.firewall is able to take one of the following values: 'disabled', 'learning', 'permissive' and 'enforcing'. The default value is 'disabled'.
sql_firewall.max
Number of queries the SQL Firewall can learn. It can take an int value between 100 and INT_MAX. The default value is 5000. The queries which exceed this value in the "learning" mode would never be learned.
sql_firewall_reset()
sql_firewall_reset() clears the firewall rules.
This function is available only under the disabled mode with superuser privilege.
sql_firewall_stat_reset()
sql_firewall_reset() clears the counters of warning and error. Only available with superuser privilege.
sql_firewall_export_rule('/path/to/rule.txt')
sql_firewall_export_rule() writes the firewall rules in the specified CSV file.
This function is available only under the disabled mode with superuser privilege.
sql_firewall_import_rule('/path/to/rule.txt')
sql_firewall_import_rule() reads the firewall rules from the specified CSV file.
This function is available only under the disabled mode with superuser privilege.
sql_firewall.sql_firewall_statements
sql_firewall_statements view shows the firewall rules and execution counter for each query.
postgres=# select from sql_firewall.sql_firewall_statements; userid | queryid | query | calls --------+------------+---------------------------------+------- 10 | 3294787656 | select from k1 where uid = ?; | 4 (1 row)
postgres=#
sql_firewall.sql_firewall_stat
sql_firewall_stat view has two counters: "sql_warning" and "sql_error".
"sql_warning" shows number of executed queries with warnings in the "permissive" mode.
"sql_error" shows number of prevented queries in the "enforcing" mode.
postgres=# select * from sql_firewall.sql_firewall_stat; sql_warning | sql_error -------------+----------- 2 | 1 (1 row)
postgres=#
Permissive mode
postgres=# select from sql_firewall.sql_firewall_statements; WARNING: Prohibited SQL statement userid | queryid | query | calls --------+------------+---------------------------------+------- 10 | 3294787656 | select from k1 where uid = 1; | 1 (1 row)
postgres=# select * from k1 where uid = 1; uid | uname -----+------------- 1 | Park Gyu-ri (1 row)
postgres=# select * from k1 where uid = 3; uid | uname -----+----------- 3 | Goo Ha-ra (1 row)
postgres=# select * from k1 where uid = 3 or 1 = 1; WARNING: Prohibited SQL statement uid | uname -----+---------------- 1 | Park Gyu-ri 2 | Nicole Jung 3 | Goo Ha-ra 4 | Han Seung-yeon 5 | Kang Ji-young (5 rows)
postgres=#
Enforcing mode
postgres=# select * from k1 where uid = 3; uid | uname -----+----------- 3 | Goo Ha-ra (1 row)
postgres=# select * from k1 where uid = 3 or 1 = 1; ERROR: Prohibited SQL statement postgres=#
Satoshi Nagayasu snaga@uptime.jp