netdev - Re: [PATCH 3/8] vhost: vringh: use krealloc

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Date:   Tue, 27 Oct 2020 17:58:43 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Joe Perches <joe@...ches.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        linux-media <linux-media@...r.kernel.org>,
        linux-drm <dri-devel@...ts.freedesktop.org>,
        linaro-mm-sig@...ts.linaro.org,
        LKML <linux-kernel@...r.kernel.org>, linux-edac@...r.kernel.org,
        linux-gpio <linux-gpio@...r.kernel.org>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        netdev <netdev@...r.kernel.org>, linux-mm@...ck.org,
        Linux-ALSA <alsa-devel@...a-project.org>
Subject: Re: [PATCH 3/8] vhost: vringh: use krealloc_array()

On Tue, Oct 27, 2020 at 5:50 PM Joe Perches <joe@...ches.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@...libre.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@...libre.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;
>  }
>
>
>