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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 13 Sep 2021 16:23:38 -0700
Message-ID: <CAKwvOdnFRhKDZ3XuePSGsuxhOpuS5RmZ1u+MeN=PRPPKSS3wFg@mail.gmail.com>
Subject: Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Arnd Bergmann <arnd@kernel.org>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Baokun Li <libaokun1@huawei.com>,
        open list <linux-kernel@vger.kernel.org>,
        linux-stable <stable@vger.kernel.org>,
        Hulk Robot <hulkci@huawei.com>,
        Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        lkft-triage@lists.linaro.org, llvm@lists.linux.dev,
        Kees Cook <keescook@chromium.org>
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On Mon, Sep 13, 2021 at 4:00 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, Sep 13, 2021 at 2:15 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > Sorry wrong diff:
>
> Well, this second diff was seriously whitespace-damaged and hard to
> read, but while it seems to be the same number of lines, it sure looks
> a lot more readable in this format.
>
> Except I think that
>
>                 default: dividend / divisor);
>
> should really have parentheses around both of those macro arguments.
>
> That's a preexisting problem, but it should be fixed while at it.

Ok, I'll send a revised v2 based on _Generic; Rasmus can help review
when he's awake.

> I'm also not sure why that (again, preexisting) BUILD_BUG_ON_MSG()
> only checks the size of the dividend, not the divisor. Very strange.
> But probably not worth worrying about.

I sent a not-yet-applied diff of my not-yet-applied diff.  I was
playing with this last week, and IIRC we had divisors that were less
than 32b being promoted to int. But I'll test it some more.
-- 
Thanks,
~Nick Desaulniers