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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Tue, 27 Oct 2020 17:58:43 +0100
Message-ID: <CAMpxmJU0C84DjPmqmWvPgv0zwgGLhkpKLRDuKkZHAa=wi+LvBA@mail.gmail.com>
Subject: Re: [PATCH 3/8] vhost: vringh: use krealloc_array()
To:     Joe Perches <joe@perches.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Gustavo Padovan <gustavo@padovan.org>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Tony Luck <tony.luck@intel.com>,
        James Morse <james.morse@arm.com>,
        Robert Richter <rric@kernel.org>,
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On Tue, Oct 27, 2020 at 5:50 PM Joe Perches <joe@perches.com> wrote:
>
> On Tue, 2020-10-27 at 11:28 -0400, Michael S. Tsirkin wrote:
> > On Tue, Oct 27, 2020 at 01:17:20PM +0100, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> > >
> > > Use the helper that checks for overflows internally instead of manually
> > > calculating the size of the new array.
> > >
> > > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > No problem with the patch, it does introduce some symmetry in the code.
>
> Perhaps more symmetry by using kmemdup
> ---
>  drivers/vhost/vringh.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index 8bd8b403f087..99222a3651cd 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -191,26 +191,23 @@ static int move_to_indirect(const struct vringh *vrh,
>  static int resize_iovec(struct vringh_kiov *iov, gfp_t gfp)
>  {
>         struct kvec *new;
> -       unsigned int flag, new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
> +       size_t new_num = (iov->max_num & ~VRINGH_IOV_ALLOCATED) * 2;
> +       size_t size;
>
>         if (new_num < 8)
>                 new_num = 8;
>
> -       flag = (iov->max_num & VRINGH_IOV_ALLOCATED);
> -       if (flag)
> -               new = krealloc(iov->iov, new_num * sizeof(struct iovec), gfp);
> -       else {
> -               new = kmalloc_array(new_num, sizeof(struct iovec), gfp);
> -               if (new) {
> -                       memcpy(new, iov->iov,
> -                              iov->max_num * sizeof(struct iovec));
> -                       flag = VRINGH_IOV_ALLOCATED;
> -               }
> -       }
> +       if (unlikely(check_mul_overflow(new_num, sizeof(struct iovec), &size)))
> +               return -ENOMEM;
> +

The whole point of using helpers such as kmalloc_array() is not doing
these checks manually.

Bartosz

> +       if (iov->max_num & VRINGH_IOV_ALLOCATED)
> +               new = krealloc(iov->iov, size, gfp);
> +       else
> +               new = kmemdup(iov->iov, size, gfp);
>         if (!new)
>                 return -ENOMEM;
>         iov->iov = new;
> -       iov->max_num = (new_num | flag);
> +       iov->max_num = new_num | VRINGH_IOV_ALLOCATED;
>         return 0;
>  }
>
>
>