linux-kernel - Re: [PATCH v2] md/raid5: Convert stripe_head's "dev" to flexible array member

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Message-ID: <202305301600.EEF0BAAD@keescook>
Date:   Tue, 30 May 2023 16:00:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Song Liu <song@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] md/raid5: Convert stripe_head's "dev" to flexible
 array member

On Tue, May 23, 2023 at 10:43:52AM -0700, Song Liu wrote:
> On Mon, May 22, 2023 at 2:21 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > Replace old-style 1-element array of "dev" in struct stripe_head with
> > modern C99 flexible array. In the future, we can additionally annotate
> > it with the run-time size, found in the "disks" member.
> >
> > Cc: Christoph Hellwig <hch@...radead.org>
> > Cc: linux-raid@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> > It looks like this memory calculation:
> >
> >         memory = conf->min_nr_stripes * (sizeof(struct stripe_head) +
> >                  max_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
> >
> > ... was already buggy (i.e. it included the single "dev" bytes in the
> > result). However, I'm not entirely sure if that is the right analysis,
> > since "dev" is not related to struct bio nor PAGE_SIZE?
> >
> > v1: https://lore.kernel.org/all/20230517233313.never.130-kees@kernel.org/
> > v2: use new struct_size_t() helper from
> >     https://lore.kernel.org/lkml/20230522211810.never.421-kees@kernel.org/
> 
> LTGM. Thanks!

Thanks!

> I will hold this for a while until struct_size_t() merged.

Since my tree will introduce struct_size_t(), I will just carry it
there.

-- 
Kees Cook