linux-kernel - Re: [GIT PULL] bcachefs fixes for 6.15-rc4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aAvlM1G1k94kvCs9@casper.infradead.org>
Date: Fri, 25 Apr 2025 20:40:35 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
	linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] bcachefs fixes for 6.15-rc4

On Fri, Apr 25, 2025 at 09:35:27AM -0700, Linus Torvalds wrote:
> Now, if filesystem people were to see the light, and have a proper and
> well-designed case insensitivity, that might change. But I've never
> seen even a *whiff* of that. I have only seen bad code that
> understands neither how UTF-8 works, nor how unicode works (or rather:
> how unicode does *not* work - code that uses the unicode comparison
> functions without a deeper understanding of what the implications
> are).
> 
> Your comments blaming unicode is only another sign of that.
> 
> Because no, the problem with bad case folding isn't in unicode.
> 
> It's in filesystem people who didn't understand - and still don't,
> after decades - that you MUST NOT just blindly follow some external
> case folding table that you don't understand and that can change over
> time.

I think this is something that NTFS actually got right.  Each filesystem
carries with it a 128KiB table that maps each codepoint to its
case-insensitive equivalent.  So there's no ambiguity about "which
version of the unicode standard are we using", "Does the user care
about Turkish language rules?", "Is Aachen a German or Danish word?".
The sysadmin specified all that when they created the filesystem, and it
doesn't matter what the Unicode standard changes in the future; if you
need to change how the filesystem sorts things, you can update the table.

It's not the perfect solution, but it might be the least-bad one I've
seen.