linux-kernel - Re: [GIT PULL] pid: use flex array

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Message-ID: <20230701-sackgasse-affront-3eb55b35bf62@brauner>
Date:   Sat, 1 Jul 2023 08:27:25 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] pid: use flex array

On Fri, Jun 30, 2023 at 09:59:47AM -0700, Kees Cook wrote:
> On Fri, Jun 30, 2023 at 10:04:14AM +0200, Christian Brauner wrote:
> > On Fri, Jun 30, 2023 at 12:12:22AM -0700, Linus Torvalds wrote:
> > > On Thu, 29 Jun 2023 at 23:51, Christian Brauner <brauner@...nel.org> wrote:
> > > >
> > > > I have no preference for either syntax. Both work. But this is probably
> > > > more an objection to this being mixed in with the flex array change in
> > > > the first place.
> > > 
> > > Yes. I looked at it, and tried to figure out if it was related
> > > somehow, and decided that no, it can't possibly be, and must be just
> > > an unrelated change.
> 
> Yes, those changes were style changes because I was annoyed that a grep
> for 'numbers[' didn't turn anything up. :P Since it's an array I think
> it's just good form to use [] when accessing an element. But yes, it's
> conceptually the same.
> 
> > > > I did react to that in the original review here:
> > > > https://lore.kernel.org/all/20230518-zuneigen-brombeeren-0a57cd32b1a7@brauner
> > > > but then I grepped for it and saw it done in a few other places already
> > > 
> > > Yeah, we do end up growing new uses of 'use 0 as a pointer' almost as
> > > quickly as we get rid of them.
> 
> Apologies on this -- this patch was just before the addition of
> struct_size_t(), so I missed it in the cleanup I did for that:
> https://git.kernel.org/linus/d67790ddf0219aa0ad3e13b53ae0a7619b3425a2
> 
> > I've grepped around a bit and I saw that the
> > struct_size((struct bla *)NULL, ...)
> > pattern seems to be used in most places that have similar needs. Not
> > sure if there's something nicer.
> 
> The above patch fixes them all (excepting struct pid). In retrospect, I
> should have asked to carry the struct pid fix in the hardening tree due
> to that.
> 
> > I gave this thing a stab myself since I have a few minutes and so Kees
> > doesn't have to do it. Authorship retained and dropped the ack. Is the
> > following more acceptable? 
> 
> Thanks for reworking it!
> 
> > [...]
> > [brauner: dropped unrelated changes and remove 0 with NULL cast]
> 
> However, this should use struct_size_t(); I'll send a new patch and
> double check that UBSAN stays happy, etc.

I think Linus already applied it let me quickly send a follow-up
replacing the two open-coded cases with struct_size_t(). I didn't know
this existed and I think when you originally send the patch it didn't.