linux-hardening - Re: [PATCH] comedi: Annotate struct comedi_lrange with __counted

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Message-ID: <alpine.DEB.2.22.394.2310020737570.3166@hadrien>
Date: Mon, 2 Oct 2023 07:38:42 +0200 (CEST)
From: Julia Lawall <julia.lawall@...ia.fr>
To: Kees Cook <keescook@...omium.org>
cc: Julia Lawall <julia.lawall@...ia.fr>, Kees Cook <kees@...nel.org>, 
    Christophe JAILLET <christophe.jaillet@...adoo.fr>, 
    Ian Abbott <abbotti@....co.uk>, 
    H Hartley Sweeten <hsweeten@...ionengravers.com>, 
    "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
    Nathan Chancellor <nathan@...nel.org>, 
    Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, 
    linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org, 
    linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] comedi: Annotate struct comedi_lrange with
 __counted_by



On Sun, 1 Oct 2023, Kees Cook wrote:

> On Sun, Oct 01, 2023 at 02:22:17PM -0700, Kees Cook wrote:
> > On Sun, Oct 01, 2023 at 02:05:46PM -0700, Kees Cook wrote:
> > > On Sun, Oct 01, 2023 at 09:14:02PM +0200, Julia Lawall wrote:
> > > > Kees,
> > > >
> > > > You can try the following.
> > >
> > > Cool! Yeah, this finds the example:
> > >
> > > drivers/comedi/drivers/rti800.c:74: struct comedi_lrange: field at offset 0 is the counter for the flex array
> > > drivers/comedi/drivers/rti800.c:83: struct comedi_lrange: field at offset 0 is the counter for the flex array
> > > drivers/comedi/drivers/rti800.c:92: struct comedi_lrange: field at offset 0 is the counter for the flex array
> > >
> > > I'll run it on the whole codebase...
> >
> > It found only the struct comedi_lrange instances, but that's good to
> > know. :)
>
> On a related note, why doesn't this work?
>
> @allocated@
> identifier STRUCT, ARRAY;
> expression COUNT;
> struct STRUCT *PTR;
> identifier ALLOC;
> type ELEMENT_TYPE;
> @@
>
>         PTR = ALLOC(..., sizeof(\(*PTR\|struct STRUCT\)) +
>                          COUNT * sizeof(\(*PTR->ARRAY\|PTR->ARRAY[0]\|ELEMENT_TYPE\)), ...);
>
>
> minus: parse error:
>   File "alloc.cocci", line 15, column 34, charpos = 485
>   around = 'struct',
>   whole content =       PTR = ALLOC(..., sizeof(\(*PTR\|struct STRUCT\)) +
>
> if I drop "struct", then it complains about ELEMENT_TYPE...

The sizeof with an expression argument is treated differently than the
sizeof with a type argument.  So you need to write:

@allocated@
identifier STRUCT, ARRAY;
expression COUNT;
struct STRUCT *PTR;
identifier ALLOC;
type ELEMENT_TYPE;
@@

        PTR = ALLOC(..., \(sizeof(*PTR)\|sizeof(struct STRUCT)\) +
                         COUNT * \(sizeof(*PTR->ARRAY)\|sizeof(PTR->ARRAY[0])\|sizeof(ELEMENT_TYPE)\), ...);

julia