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In-Reply-To: <db321a38-f5f6-34cd-2f4f-37fc82201798@huawei.com>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 13 Sep 2021 20:30:46 -0700
Message-ID: <CAKwvOdmMHFOke5kzzgBDwKySzP799-cnp-61cohJRJTS4cFmzQ@mail.gmail.com>
Subject: Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()
To:     "libaokun (A)" <libaokun1@huawei.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        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>,
        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 7:13 PM libaokun (A) <libaokun1@huawei.com> wrote:
>
> =E5=9C=A8 2021/9/14 7:23, Nick Desaulniers =E5=86=99=E9=81=93:
> > 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.
>
> How about deleting the check_mul_overflow in the __nbd_ioctl as follows?
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 5170a630778d..f404e0540476 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1393,7 +1393,6 @@ static int __nbd_ioctl(struct block_device *bdev,
> struct nbd_device *nbd,
>                         unsigned int cmd, unsigned long arg)
>   {
>          struct nbd_config *config =3D nbd->config;
> -       loff_t bytesize;
>
>          switch (cmd) {
>          case NBD_DISCONNECT:
> @@ -1408,9 +1407,10 @@ static int __nbd_ioctl(struct block_device *bdev,
> struct nbd_device *nbd,
>          case NBD_SET_SIZE:
>                  return nbd_set_size(nbd, arg, config->blksize);
>          case NBD_SET_SIZE_BLOCKS:
> -               if (check_mul_overflow((loff_t)arg, config->blksize,
> &bytesize))
> +               if (arg && (LLONG_MAX / arg <=3D config->blksize))
>                          return -EINVAL;

64b division is going to need do_div(), yeah? Besides, this is likely
to pop up again for other callers of check_mul_overflow(), might as
well fix it.

> -               return nbd_set_size(nbd, bytesize, config->blksize);
> +               return nbd_set_size(nbd, arg * config->blksize,
> +                                   config->blksize);
>          case NBD_SET_TIMEOUT:
>                  nbd_set_cmd_timeout(nbd, arg);
>                  return 0;
> --
> 2.31.1
>
> --
> With Best Regards,
> Baokun Li
>
>
>


--=20
Thanks,
~Nick Desaulniers