linux-hardening - Re: [PATCH v2] tty: rfcomm: prefer struct

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Date: Mon, 13 May 2024 11:51:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Erick Archer <erick.archer@...look.com>
Cc: Jiri Slaby <jirislaby@...nel.org>,
	Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	"David S.  Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH v2] tty: rfcomm: prefer struct_size over open coded
 arithmetic

On Mon, May 13, 2024 at 07:12:57PM +0200, Erick Archer wrote:
> Hi Kees, Jiri and Luiz,
> First of all, thanks for the reviews.
> 
> On Mon, May 13, 2024 at 12:29:04PM -0400, Luiz Augusto von Dentz wrote:
> > Hi Jiri, Eric,
> > 
> > On Mon, May 13, 2024 at 1:07 AM Jiri Slaby <jirislaby@...nel.org> wrote:
> > >
> > > On 12. 05. 24, 13:17, Erick Archer wrote:
> > > > This is an effort to get rid of all multiplications from allocation
> > > > functions in order to prevent integer overflows [1][2].
> > > >
> > > > As the "dl" variable is a pointer to "struct rfcomm_dev_list_req" and
> > > > this structure ends in a flexible array:
> > > ...
> > > > --- a/include/net/bluetooth/rfcomm.h
> > > > +++ b/include/net/bluetooth/rfcomm.h
> > > ...
> > > > @@ -528,12 +527,12 @@ static int rfcomm_get_dev_list(void __user *arg)
> > > >       list_for_each_entry(dev, &rfcomm_dev_list, list) {
> > > >               if (!tty_port_get(&dev->port))
> > > >                       continue;
> > > > -             (di + n)->id      = dev->id;
> > > > -             (di + n)->flags   = dev->flags;
> > > > -             (di + n)->state   = dev->dlc->state;
> > > > -             (di + n)->channel = dev->channel;
> > > > -             bacpy(&(di + n)->src, &dev->src);
> > > > -             bacpy(&(di + n)->dst, &dev->dst);
> > > > +             di[n].id      = dev->id;
> > > > +             di[n].flags   = dev->flags;
> > > > +             di[n].state   = dev->dlc->state;
> > > > +             di[n].channel = dev->channel;
> > > > +             bacpy(&di[n].src, &dev->src);
> > > > +             bacpy(&di[n].dst, &dev->dst);
> > >
> > > This does not relate much to "prefer struct_size over open coded
> > > arithmetic". It should have been in a separate patch.
> > 
> > +1, please split these changes into its own patch so we can apply it separately.
> 
> Ok, no problem. Also, I will simplify the "bacpy" lines with direct
> assignments as Kees suggested:
> 
>    di[n].src = dev->src;
>    di[n].dst = dev->dst;
> 
> instead of:
> 
>    bacpy(&di[n].src, &dev->src);
>    bacpy(&di[n].dst, &dev->dst);

I think that's a separate thing and you can leave bacpy() as-is for now.

-- 
Kees Cook