Re: [PATCH] misc: mic: fix a DMA pool free failure

[Wenwen Wang <wang6495@umn.edu>]

On Sun, Nov 4, 2018 at 8:05 PM Sudeep Dutt <sudeep.dutt@intel.com> wrote:
>
> On Thu, 2018-10-18 at 14:46 -0500, Wenwen Wang wrote:
> > In _scif_prog_signal(), a DMA pool is allocated if the MIC Coprocessor is
> > not X100, i.e., the boolean variable 'x100' is false. This DMA pool will be
> > freed eventually through the callback function scif_prog_signal_cb() with
> > the parameter of 'status', which actually points to the start of DMA pool.
> > Specifically, in scif_prog_signal_cb(), the 'ep' field and the
> > 'src_dma_addr' field of 'status' are used to free the DMA pool by invoking
> > dma_pool_free(). Given that 'status' points to the start address of the DMA
> > pool, both 'status->ep' and 'status->src_dma_addr' are in the DMA pool. And
> > so, the device has the permission to access them. Even worse, a malicious
> > device can modify them. As a result, dma_pool_free() will not succeed.
> >
> > To avoid the above issue, this patch introduces a new data structure, i.e.,
> > scif_cb_arg, to store the arguments required by the call back function. A
> > variable 'cb_arg' is allocated in _scif_prog_signal() to pass the
> > arguments. 'cb_arg' will be freed after dma_pool_free() in
> > scif_prog_signal_cb().
> >
> > Signed-off-by: Wenwen Wang <wang6495@umn.edu>
> > ---
> >  drivers/misc/mic/scif/scif_fence.c | 17 +++++++++++++----
> >  drivers/misc/mic/scif/scif_rma.h   | 14 ++++++++++++++
> >  2 files changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/misc/mic/scif/scif_fence.c b/drivers/misc/mic/scif/scif_fence.c
> > index cac3bcc..30f7d9b 100644
> > --- a/drivers/misc/mic/scif/scif_fence.c
> > +++ b/drivers/misc/mic/scif/scif_fence.c
> > @@ -195,10 +195,11 @@ static inline void *scif_get_local_va(off_t off, struct scif_window *window)
> >
> >  static void scif_prog_signal_cb(void *arg)
> >  {
> > -     struct scif_status *status = arg;
> > +     struct scif_cb_arg *cb_arg = arg;
> >
> > -     dma_pool_free(status->ep->remote_dev->signal_pool, status,
> > -                   status->src_dma_addr);
> > +     dma_pool_free(cb_arg->ep->remote_dev->signal_pool, cb_arg->status,
> > +                   cb_arg->src_dma_addr);
> > +     kfree(cb_arg);
> >  }
> >
> >  static int _scif_prog_signal(scif_epd_t epd, dma_addr_t dst, u64 val)
> > @@ -209,6 +210,7 @@ static int _scif_prog_signal(scif_epd_t epd, dma_addr_t dst, u64 val)
> >       bool x100 = !is_dma_copy_aligned(chan->device, 1, 1, 1);
> >       struct dma_async_tx_descriptor *tx;
> >       struct scif_status *status = NULL;
> > +     struct scif_cb_arg *cb_arg = NULL;
> >       dma_addr_t src;
> >       dma_cookie_t cookie;
> >       int err;
> > @@ -257,8 +259,15 @@ static int _scif_prog_signal(scif_epd_t epd, dma_addr_t dst, u64 val)
> >               goto dma_fail;
> >       }
> >       if (!x100) {
> > +             err = -ENOMEM;
>
> Should err be set to -ENOMEM only if the cb_arg allocation fails?
>
> > +             cb_arg = kmalloc(sizeof(*cb_arg), GFP_KERNEL);
> > +             if (!cb_arg)
> > +                     goto dma_fail;
> > +             cb_arg->src_dma_addr = src;
> > +             cb_arg->status = status;
> > +             cb_arg->ep = ep;
> >               tx->callback = scif_prog_signal_cb;
> > -             tx->callback_param = status;
> > +             tx->callback_param = cb_arg;
> >       }
>
> cb_arg should be freed if there is a dma_submit_error(..) below in the
> dma_fail path.
>
> Wenwen, can you please fix these up and resend the patch?

Sure, will fix the issues and resubmit the patch. Thanks!

Wenwen