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

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Date:   Sun, 29 Sep 2019 21:22:56 -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

It is a neat fix now, thank you.


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.