linux-kernel - Re: [PATCH 47/64] btrfs: Use memset

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Date:   Mon, 9 Aug 2021 13:20:30 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH 47/64] btrfs: Use memset_after() to clear end of struct

On Sat, Jul 31, 2021 at 08:25:51AM -0700, Kees Cook wrote:
> On Thu, Jul 29, 2021 at 12:33:37PM +0200, David Sterba wrote:
> > On Wed, Jul 28, 2021 at 02:56:31PM -0700, Kees Cook wrote:
> > > On Wed, Jul 28, 2021 at 11:42:15AM +0200, David Sterba wrote:
> > > > On Tue, Jul 27, 2021 at 01:58:38PM -0700, Kees Cook wrote:
> > > > >  	}
> > > > >  	if (need_reset) {
> > > > > -		memset(&item->generation_v2, 0,
> > > > > -			sizeof(*item) - offsetof(struct btrfs_root_item,
> > > > > -					generation_v2));
> > > > > -
> > > > 
> > > > Please add
> > > > 		/* Clear all members from generation_v2 onwards */
> > > > 
> > > > > +		memset_after(item, 0, level);
> > > 
> > > Perhaps there should be another helper memset_starting()? That would
> > > make these cases a bit more self-documenting.
> > 
> > That would be better, yes.
> > 
> > > +		memset_starting(item, 0, generation_v2);
> > 
> > memset_from?
> 
> For v2, I bikeshed this to "memset_startat" since "from" is semantically
> close to "source" which I thought might be confusing. (I, too, did not
> like "starting".) :)

memset_startat works for me, thanks.