Re: BUG #19354: JOHAB rejects valid byte sequences

On Tue, Dec 16, 2025 at 10:41 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> However, that doesn't mean we can fix pg_johab_mblen() and we're done.
> I'm still quite afraid that we'd be introducing security-grade
> inconsistencies of interpretation between different PG versions.

I understand that fear, but I do not have an opinion either way on
whether there would be an actual vulnerability

I think there is a good chance that the right going-forward fix is to
deprecate the encoding, because according to
https://www.unicode.org/Public/MAPPINGS/EASTASIA/ReadMe.txt this and
everything else that's now under
https://www.unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/ were
deprecated in 2001. By the time v19 is released, the deprecation will
be a quarter-century old, and the fact that it doesn't work is good
evidence that few people will miss it, though perhaps the original
poster will want to put forward an argument for why we should still
care about this.

What to do in the back branches is a more difficult question. Since
this is a client-only encoding, there's no issue of what is already
stored in the database, and we would not be proposing to change any of
the mappings, just allow the ones that don't currently work to do so.
I *think* that fixing pg_johab_mblen() would be "forward compatible":
the subset of the encoding that already works would continue to behave
in the same way, and the rest of it would begin working as well.

And, I don't really like throwing up our hands and deciding that
already-released features are free to continue not working. That's
what bug-fix release are for.

On the other hand, fixing this bug which apparently affects very few
users, and in the process creating a scarier, CVE-worthy bug would not
win us many friends, especially in view of the apparently-low uptake
of this encoding.

--
Robert Haas
EDB: http://www.enterprisedb.com