From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Don't rely on zlib's gzgetc() macro.
Date: Sun, 19 Oct 2025 18:37:15 +0000
Message-ID: <E1vAYHL-002UWH-0G@gemulon.postgresql.org> (raw)
Don't rely on zlib's gzgetc() macro.
It emerges that zlib's configuration logic is not robust enough
to guarantee that the macro will have the same ideas about struct
field layout as the library itself does, leading to corruption of
zlib's state struct followed by unintelligible failure messages.
This hazard has existed for a long time, but we'd not noticed
for several reasons:
(1) We only use gzgetc() when trying to read a manually-compressed
TOC file within a directory-format dump, which is a rarely-used
scenario that we weren't even testing before 20ec99589.
(2) No corruption actually occurs unless sizeof(long) is different
from sizeof(off_t) and the platform is big-endian.
(3) Some platforms have already fixed the configuration instability,
at least sufficiently for their environments.
Despite (3), it seems foolish to assume that the problem isn't
going to be present in some environments for a long time to come.
Hence, avoid relying on this macro. We can just #undef it and
fall back on the underlying function of the same name.
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/2122679.1760846783@sss.pgh.pa.us
Backpatch-through: 13
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/277dec6514728e2d0d87c1279dd5e0afbf897428
Modified Files
--------------
src/bin/pg_dump/compress_gzip.c | 9 +++++++++
1 file changed, 9 insertions(+)
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: Don't rely on zlib's gzgetc() macro.
In-Reply-To: <E1vAYHL-002UWH-0G@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