linux-kernel - Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd

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Message-ID: <CAKwvOdkf3B41RRe8FDkw1H-0hBt1_PhZtZxBZ5pj0pyh7vDLmA@mail.gmail.com>
Date:   Mon, 13 Sep 2021 13:16:21 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...nel.org>
Cc:     Sedat Dilek <sedat.dilek@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Baokun Li <libaokun1@...wei.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-stable <stable@...r.kernel.org>,
        Hulk Robot <hulkci@...wei.com>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        lkft-triage@...ts.linaro.org, llvm@...ts.linux.dev,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()

On Mon, Sep 13, 2021 at 1:10 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Mon, Sep 13, 2021 at 1:02 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > Ha! I pulled+rebased and this code disappeared...I thought I had
> > rebased on the wrong branch or committed work to master accidentally.
> > Patch to stable-only inbound.
>
> Side note: for stable, can you look into using _Generic() instead of
> __builtin_choose_expression() with typeof, or some
> __builtin_types_compatible_p() magic?
>
> Yes, yes, we use __builtin_choose_expression() elsewhere, but we've
> started using _Generic(), and it's really the more natural model - in
> addition to being the standard C one.
>
> Of course, there may be some reason why _Generic() doesn't work, but
> it _is_ the natural fit for any "for type X, do Y" kind of thing.
>
> No?

Man, c'mon, I just got the __builtin_choose_expression() working! It's
not...too bad...ish. (Besides, I'd actually have to learn how to use
_Generic...I've never quite gotten anything I've written trying to use
it to actually compile).

Do we have access to _Generic in GCC 4.9?
-- 
Thanks,
~Nick Desaulniers