linux-kernel - Re: [GIT PULL] bcachefs updates for 6.8

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Date: Thu, 11 Jan 2024 16:18:37 -0800
From: Kees Cook <keescook@...omium.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Matthew Wilcox <willy@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [GIT PULL] bcachefs updates for 6.8

On Thu, Jan 11, 2024 at 07:05:06PM -0500, Kent Overstreet wrote:
> On Thu, Jan 11, 2024 at 03:42:19PM -0800, Kees Cook wrote:
> > On Thu, Jan 11, 2024 at 10:57:18PM +0000, Matthew Wilcox wrote:
> > > On Wed, Jan 10, 2024 at 05:47:20PM -0800, Linus Torvalds wrote:
> > > > No, because the whole idea of "let me mark something deprecated and
> > > > then not just remove it" is GARBAGE.
> > > > 
> > > > If somebody wants to deprecate something, it is up to *them* to finish
> > > > the job. Not annoy thousands of other developers with idiotic
> > > > warnings.
> > > 
> > > What would be nice is something that warned about _new_ uses being
> > > added.  ie checkpatch.  Let's at least not make the problem worse.
> > 
> > For now, we've just kind of "dealt with it". For things that show up
> > with new -W options we've enlisted sfr to do the -next builds with it
> > explicitly added (but not to the tree) so he could generate nag emails
> > when new warnings appeared. That could happen if we added it to W=1
> > builds, or some other flag like REPORT_DEPRECATED=1.
> > 
> > Another ugly idea would be to do a treewide replacement of "func" to
> > "func_deprecated", and make "func" just a wrapper for it that is marked
> > with __deprecated. Then only new instances would show up (assuming people
> > weren't trying to actively bypass the deprecation work by adding calls to
> > "func_deprecated"). :P Then the refactoring to replace "func_deprecated"
> > could happen a bit more easily.
> > 
> > Most past deprecations have pretty narrow usage. This is not true with
> > the string functions, which is why it's more noticeable here. :P
> 
> Before doing the renaming - why not just leave a kdoc comment that marks
> it as deprecated? Seems odd that checkpatch was patched, but I can't
> find anything marking it as deprecated when I cscope to it.

It doesn't explicitly say "deprecated", but this language has been in
the kdoc for a while now (not that people go read this often):

 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * over-reads when calculating strlen(@q), it is still possible.
 * Prefer strscpy(), though note its different return values for
 * detecting truncation.

But it's all fine -- we're about to wipe out strlcpy for v6.8. Once the
drivers-core and drm-misc-next trees land, (and the bcachefs patch[1])
we'll be at 0 users. :)

-Kees

[1] https://lore.kernel.org/lkml/20240110235438.work.385-kees@kernel.org/

-- 
Kees Cook