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

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Date:   Mon, 13 Sep 2021 13:02:32 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     sedat.dilek@...il.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.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 12:57 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> On Mon, Sep 13, 2021 at 9:53 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@...glegroups.com> wrote:
> >
> > On Mon, Sep 13, 2021 at 11:39 AM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> > >
> > > There's an issue with my alternative approach
> > > (https://gist.github.com/nickdesaulniers/2479818f4983bbf2d688cebbab435863)
> > > with declaring the local variable z in div_64() since either operand
> > > could be 64b, which result in an unwanted truncation if the dividend
> > > is 32b (or less, and divisor is 64b). I think (what I realized this
> > > weekend) is that we might be able to replace the `if` with
> > > `__builtin_choose_expr`, then have that whole expression be the final
> > > statement and thus the "return value" of the statement expression.
> >
> > Christ...that...works? Though, did Linus just merge my patches for gcc 5.1?
> >
>
> "Merge branch 'gcc-min-version-5.1' (make gcc-5.1 the minimum version)"

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.
-- 
Thanks,
~Nick Desaulniers