linux-kernel - Re: [PATCH] virt: vbox: fix memory leak in hgcm_call_preprocess

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Date:   Mon, 30 Sep 2019 15:43:26 -0500
From:   Navid Emamdoost <navid.emamdoost@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Navid Emamdoost <emamd001@....edu>, kjlu@....edu,
        Stephen McCamant <smccaman@....edu>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virt: vbox: fix memory leak in hgcm_call_preprocess_linaddr

On Mon, Sep 30, 2019 at 3:22 AM Hans de Goede <hdegoede@...hat.com> wrote:
>
> Hi,
>
> On 30-09-2019 04:22, Navid Emamdoost wrote:
> > It is a neat fix now, thank you.
>
> Can you submit a new version of your patch with the fix I proposed please ?
>
> Regards,
>
> Hans
>

Sure, v2 was sent.

>
> >
> >
> > On Sat, Sep 28, 2019 at 4:54 AM Hans de Goede <hdegoede@...hat.com> wrote:
> >>
> >> Hi,
> >>
> >> On 28-09-2019 01:04, Navid Emamdoost wrote:
> >>> In hgcm_call_preprocess_linaddr memory is allocated for bounce_buf but
> >>> is not released if copy_form_user fails. The release is added.
> >>>
> >>> Fixes: 579db9d45cb4 ("virt: Add vboxguest VMMDEV communication code")
> >>>
> >>> Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> >>
> >> Thank you for catching this, I agree this is a bug, but I think we
> >> can fix it in a cleaner way (see below).
> >>
> >>> ---
> >>>    drivers/virt/vboxguest/vboxguest_utils.c | 4 +++-
> >>>    1 file changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/virt/vboxguest/vboxguest_utils.c b/drivers/virt/vboxguest/vboxguest_utils.c
> >>> index 75fd140b02ff..7965885a50fa 100644
> >>> --- a/drivers/virt/vboxguest/vboxguest_utils.c
> >>> +++ b/drivers/virt/vboxguest/vboxguest_utils.c
> >>> @@ -222,8 +222,10 @@ static int hgcm_call_preprocess_linaddr(
> >>>
> >>>        if (copy_in) {
> >>>                ret = copy_from_user(bounce_buf, (void __user *)buf, len);
> >>> -             if (ret)
> >>> +             if (ret) {
> >>> +                     kvfree(bounce_buf);
> >>>                        return -EFAULT;
> >>> +             }
> >>>        } else {
> >>>                memset(bounce_buf, 0, len);
> >>>        }
> >>>
> >>
> >> First let me quote some more of the function, pre leak fix, for context:
> >>
> >>          bounce_buf = kvmalloc(len, GFP_KERNEL);
> >>          if (!bounce_buf)
> >>                  return -ENOMEM;
> >>
> >>          if (copy_in) {
> >>                  ret = copy_from_user(bounce_buf, (void __user *)buf, len);
> >>                  if (ret)
> >>                          return -EFAULT;
> >>          } else {
> >>                  memset(bounce_buf, 0, len);
> >>          }
> >>
> >>          *bounce_buf_ret = bounce_buf;
> >>
> >> This function gets called repeatedly by hgcm_call_preprocess(), and the
> >> caller of hgcm_call_preprocess() already takes care of freeing the
> >> bounce bufs both on a (later) error and on success:
> >>
> >>          ret = hgcm_call_preprocess(parms, parm_count, &bounce_bufs, &size);
> >>          if (ret) {
> >>                  /* Even on error bounce bufs may still have been allocated */
> >>                  goto free_bounce_bufs;
> >>          }
> >>
> >>          ...
> >>
> >> free_bounce_bufs:
> >>          if (bounce_bufs) {
> >>                  for (i = 0; i < parm_count; i++)
> >>                          kvfree(bounce_bufs[i]);
> >>                  kfree(bounce_bufs);
> >>          }
> >>
> >> So we are already taking care of freeing bounce-bufs allocated for previous
> >> parameters to the call (which me must do anyways), so a cleaner fix would
> >> be to store the allocated bounce_buf in the bounce_bufs array before
> >> doing the copy_from_user, then if copy_from_user fails it will be cleaned
> >> up by the code at the free_bounce_bufs label.
> >>
> >> IOW I believe it is better to fix this by changing the part of
> >> hgcm_call_preprocess_linaddr I quoted to:
> >>
> >>          bounce_buf = kvmalloc(len, GFP_KERNEL);
> >>          if (!bounce_buf)
> >>                  return -ENOMEM;
> >>
> >>          *bounce_buf_ret = bounce_buf;
> >>
> >>          if (copy_in) {
> >>                  ret = copy_from_user(bounce_buf, (void __user *)buf, len);
> >>                  if (ret)
> >>                          return -EFAULT;
> >>          } else {
> >>                  memset(bounce_buf, 0, len);
> >>          }
> >>
> >> This should also fix the leak in IMHO is a clear way of doing so.
> >>
> >> Regards,
> >>
> >> Hans
> >>
> >>
> >>
> >>
> >>
> >
> >
>


-- 
Navid.