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Date:   Sun, 01 Oct 2023 08:26:56 -0700
From:   Kees Cook <kees@kernel.org>
To:     Julia Lawall <julia.lawall@inria.fr>,
        Kees Cook <keescook@chromium.org>
CC:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Ian Abbott <abbotti@mev.co.uk>,
        H Hartley Sweeten <hsweeten@visionengravers.com>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org, linux-hardening@vger.kernel.org,
        llvm@lists.linux.dev
Subject: Re: [PATCH] comedi: Annotate struct comedi_lrange with __counted_by
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On October 1, 2023 12:45:41 AM PDT, Julia Lawall <julia=2Elawall@inria=2Efr=
> wrote:
>
>
>On Sat, 30 Sep 2023, Kees Cook wrote:
>
>> On Sat, Sep 30, 2023 at 11:14:47AM +0200, Christophe JAILLET wrote:
>> > Prepare for the coming implementation by GCC and Clang of the __count=
ed_by
>> > attribute=2E Flexible array members annotated with __counted_by can h=
ave
>> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_B=
OUNDS
>> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-fam=
ily
>> > functions)=2E
>> >
>> > Signed-off-by: Christophe JAILLET <christophe=2Ejaillet@wanadoo=2Efr>
>> > ---
>> > This patch is part of a work done in parallel of what is currently wo=
rked
>> > on by Kees Cook=2E
>> >
>> > My patches are only related to corner cases that do NOT match the
>> > semantic of his Coccinelle script[1]=2E
>>
>> Nice!
>>
>> struct comedi_lrange {
>>         int length;
>>         struct comedi_krange range[];
>> };
>> =2E=2E=2E
>> static const struct comedi_lrange range_rti800_ai_10_bipolar =3D {
>>         4, {
>>                 BIP_RANGE(10),
>>                 BIP_RANGE(1),
>>                 BIP_RANGE(0=2E1),
>>                 BIP_RANGE(0=2E02)
>>         }
>> };
>>
>> I'm struggling to come up with a way for Coccinelle to find this kind o=
f
>> thing in other places=2E=2E=2E
>
>Kees, what exactly are you trying to match?  Static allocations?

I need to count the number of initialized elements in the flexible array t=
hat is the last member and see if it matches a value set in another member=
=2E

E=2Eg=2E the above sets 4 values for the last array member and then sets a=
nother member to 4=2E

-Kees


--=20
Kees Cook