From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Replace usages of xmlXPathCompile() with xmlXPathCtxtCompile().
Date: Sun, 15 Sep 2024 17:33:26 +0000
Message-ID: <E1spt7m-001Fk1-Fp@gemulon.postgresql.org> (raw)
Replace usages of xmlXPathCompile() with xmlXPathCtxtCompile().
In existing releases of libxml2, xmlXPathCompile can be driven
to stack overflow because it fails to protect itself against
too-deeply-nested input. While there is an upstream fix as of
yesterday, it will take years for that to propagate into all
shipping versions. In the meantime, we can protect our own
usages basically for free by calling xmlXPathCtxtCompile instead.
(The actual bug is that libxml2 keeps its nesting counter in the
xmlXPathContext, and its parsing code was willing to just skip
counting nesting levels if it didn't have a context. So if we supply
a context, all is well. It seems odd actually that it works at all
to not supply a context, because this means that XPath parsing does
not have access to XML namespace info. Apparently libxml2 never
checks namespaces until runtime? Anyway, this seems like good
future-proofing even if its only immediate effect is to dodge a bug.)
Sadly, this hack only offers protection with libxml2 2.9.11 and newer.
Before that there are multiple similar problems, so if you are
processing untrusted XML it behooves you to get a newer version.
But we have some pretty old libxml2 in the buildfarm, so it seems
impractical to add a regression test to verify this fix.
Per bug #18617 from Jingzhou Fu. Back-patch to all supported
versions.
Discussion: https://postgr.es/m/18617-1cee4d2ed1f4e7ae@postgresql.org
Discussion: https://gitlab.gnome.org/GNOME/libxml2/-/issues/799
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/4c9bf947a9ecccc8fc6f7f531530656c5b99a93c
Modified Files
--------------
contrib/xml2/xpath.c | 4 ++--
src/backend/utils/adt/xml.c | 18 +++++++++++++++---
2 files changed, 17 insertions(+), 5 deletions(-)
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: Replace usages of xmlXPathCompile() with xmlXPathCtxtCompile().
In-Reply-To: <E1spt7m-001Fk1-Fp@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