From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Avoid assertion due to disconnected NFA sub-graphs in regex pars
Date: Fri, 15 Nov 2024 23:23:56 +0000
Message-ID: <E1tC5fQ-00209P-4p@gemulon.postgresql.org> (raw)
Avoid assertion due to disconnected NFA sub-graphs in regex parsing.
In commit 08c0d6ad6 which introduced "rainbow" arcs in regex NFAs,
I didn't think terribly hard about what to do when creating the color
complement of a rainbow arc. Clearly, the complement cannot match any
characters, and I took the easy way out by just not building any arcs
at all in the complement arc set. That mostly works, but Nikolay
Shaplov found a case where it doesn't: if we decide to delete that
sub-NFA later because it's inside a "{0}" quantifier, delsub()
suffered an assertion failure. That's because delsub() relies on
the target sub-NFA being fully connected. That was always true
before, and the best fix seems to be to restore that property.
Hence, invent a new arc type CANTMATCH that can be generated in
place of an empty color complement, and drop it again later when we
start NFA optimization. (At that point we don't need to do delsub()
any more, and besides there are other cases where NFA optimization can
lead to disconnected subgraphs.)
It appears that this bug has no consequences in a non-assert-enabled
build: there will be some transiently leaked NFA states/arcs, but
they'll get cleaned up eventually. Still, we don't like assertion
failures, so back-patch to v14 where rainbow arcs were introduced.
Per bug #18708 from Nikolay Shaplov.
Discussion: https://postgr.es/m/18708-f94f2599c9d2c005@postgresql.org
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/b6312becc81949381046159c488809f8baefd2f2
Modified Files
--------------
src/backend/regex/regc_color.c | 18 +++++++++-
src/backend/regex/regc_nfa.c | 40 ++++++++++++++++++++++
src/backend/regex/regcomp.c | 3 ++
src/include/regex/regguts.h | 2 ++
.../modules/test_regex/expected/test_regex.out | 14 ++++++++
src/test/modules/test_regex/sql/test_regex.sql | 3 ++
6 files changed, 79 insertions(+), 1 deletion(-)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Avoid assertion due to disconnected NFA sub-graphs in regex pars
In-Reply-To: <E1tC5fQ-00209P-4p@gemulon.postgresql.org>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox