Re: [PATCH] virt: vbox: fix memory leak in hgcm_call_preprocess_linaddr

[Hans de Goede]

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


> On Sat, Sep 28, 2019 at 4:54 AM Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxx>
> >
> > 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