Add support for regexps on database and user entries in pg_hba.conf

Enterprise / PostgreSQL - Michael Paquier [] - 24 October 2022 02:45 UTC

As of this commit, any database or user entry beginning with a slash (/) is considered as a regular expression. This is particularly useful for users, as now there is no clean way to match pattern on multiple HBA lines. For example, a user name mapping with a regular expression needs first to match with a HBA line, and we would skip the follow-up HBA entries if the ident regexp does *not* match with what has matched in the HBA line.

pg_hba.conf is able to handle multiple databases and roles with a comma-separated list of these, hence individual regular expressions that include commas need to be double-quoted.

At authentication time, user and database names are now checked in the following order:- Arbitrary keywords (like "all", the ones beginning by '+' for membership check), that we know will never have a regexp. A fancy case is for physical WAL senders, we *have* to only match "replication" for the database.
- Regular expression matching.
- Exact match. The previous logic did the same, but without the regexp step.

We have discussed as well the possibility to support regexp pattern matching for host names, but these happen to lead to tricky issues based on what I understand, particularly with host entries that have CIDRs.

This commit relies heavily on the refactoring done in a903971 and fc579e1, so as the amount of code required to compile and execute regular expressions is now minimal. When parsing pg_hba.conf, all the computed regexps needs to explicitely free()'d, same as pg_ident.conf.

Documentation and TAP tests are added to cover this feature, including cases where the regexps use commas (for clarity in the docs, coverage for the parsing logic in the tests).

Note that this introduces a breakage with older versions, where a database or user name beginning with a slash are treated as something to check for an equal match. Per discussion, we have discarded this as being much of an issue in practice as it would require a cluster to have database and/or role names that begin with a slash, as well as HBA entries using these. Hence, the consistency gained with regexps in pg_ident.conf is more appealing in the long term.

**This compatibility change should be mentioned in the release notes.**

Author: Bertrand Drouvot

8fea86830e Add support for regexps on database and user entries in pg_hba.conf
doc/src/sgml/client-auth.sgml | 56 +++++++++++++++-----
src/backend/libpq/hba.c | 86 ++++++++++++++++++++++++++++---
src/test/authentication/t/ | 42 +++++++++++++++
3 files changed, 163 insertions(+), 21 deletions(-)


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