linux-kernel - Re: [PATCH v2] misc: mic: fix a DMA pool free failure

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Date:   Wed, 02 Jan 2019 17:50:47 -0800
From:   Sudeep Dutt <sudeep.dutt@...el.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Sudeep Dutt <sudeep.dutt@...el.com>, Kangjie Lu <kjlu@....edu>,
        Ashutosh Dixit <ashutosh.dixit@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] misc: mic: fix a DMA pool free failure

On Tue, 2018-12-04 at 09:16 -0600, 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().
> 

Thanks for incorporating the previous feedback Wenwen.

Reviewed-by: Sudeep Dutt <sudeep.dutt@...el.com>

> Signed-off-by: Wenwen Wang <wang6495@....edu>
> ---
>  drivers/misc/mic/scif/scif_fence.c | 22 +++++++++++++++++-----
>  drivers/misc/mic/scif/scif_rma.h   | 13 +++++++++++++
>  2 files changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/misc/mic/scif/scif_fence.c b/drivers/misc/mic/scif/scif_fence.c
> index 7bb929f..2e7ce6a 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 +259,16 @@ static int _scif_prog_signal(scif_epd_t epd, dma_addr_t dst, u64 val)
>  		goto dma_fail;
>  	}
>  	if (!x100) {
> +		cb_arg = kmalloc(sizeof(*cb_arg), GFP_KERNEL);
> +		if (!cb_arg) {
> +			err = -ENOMEM;
> +			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;
>  	}
>  	cookie = tx->tx_submit(tx);
>  	if (dma_submit_error(cookie)) {
> @@ -270,9 +280,11 @@ static int _scif_prog_signal(scif_epd_t epd, dma_addr_t dst, u64 val)
>  	dma_async_issue_pending(chan);
>  	return 0;
>  dma_fail:
> -	if (!x100)
> +	if (!x100) {
>  		dma_pool_free(ep->remote_dev->signal_pool, status,
>  			      src - offsetof(struct scif_status, val));
> +		kfree(cb_arg);
> +	}
>  alloc_fail:
>  	return err;
>  }
> diff --git a/drivers/misc/mic/scif/scif_rma.h b/drivers/misc/mic/scif/scif_rma.h
> index fa67222..84af303 100644
> --- a/drivers/misc/mic/scif/scif_rma.h
> +++ b/drivers/misc/mic/scif/scif_rma.h
> @@ -206,6 +206,19 @@ struct scif_status {
>  };
>  
>  /*
> + * struct scif_cb_arg - Stores the argument of the callback func
> + *
> + * @src_dma_addr: Source buffer DMA address
> + * @status: DMA status
> + * @ep: SCIF endpoint
> + */
> +struct scif_cb_arg {
> +	dma_addr_t src_dma_addr;
> +	struct scif_status *status;
> +	struct scif_endpt *ep;
> +};
> +
> +/*
>   * struct scif_window - Registration Window for Self and Remote
>   *
>   * @nr_pages: Number of pages which is defined as a s64 instead of an int