Re: [PATCH v6 3/8] bus: mhi: core: Add range check for channel id received in event ring

[Manivannan Sadhasivam]

On Tue, May 05, 2020 at 03:47:07PM -0700, Bhaumik Bhatt wrote:
> From: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
> 
> MHI data completion handler function reads channel id from event
> ring element. Value is under the control of MHI devices and can be
> any value between 0 and 255. In order to prevent out of bound access
> add a bound check against the max channel supported by controller
> and skip processing of that event ring element.
> 
> Signed-off-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
> Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> Reviewed-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
> ---
>  drivers/bus/mhi/core/main.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 605640c..e60ab21 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -776,6 +776,9 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>  		case MHI_PKT_TYPE_TX_EVENT:
>  			chan = MHI_TRE_GET_EV_CHID(local_rp);
>  			mhi_chan = &mhi_cntrl->mhi_chan[chan];

Check should be done before this statement, isn't it?

> +			if (WARN_ON(chan >= mhi_cntrl->max_chan))
> +				goto next_event;
> +

I don't prefer using gotos for non exit paths but I don't have a better solution
here. But you can try to wrap 'WARN_ON' inside the 'MHI_TRE_GET_EV_CHID'
definition and the just use:

			/*
			 * Only process the event ring elements whose channel
			 * ID is within the maximum supported range.
			 */
			if (chan < mhi_cntrl->max_chan) {
                        	mhi_chan = &mhi_cntrl->mhi_chan[chan];
                        	parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
                        	event_quota--;
			}
			break;

This looks more clean.

>  			parse_xfer_event(mhi_cntrl, local_rp, mhi_chan);
>  			event_quota--;
>  			break;
> @@ -784,6 +787,7 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>  			break;
>  		}
>  
> +next_event:
>  		mhi_recycle_ev_ring_element(mhi_cntrl, ev_ring);
>  		local_rp = ev_ring->rp;
>  		dev_rp = mhi_to_virtual(ev_ring, er_ctxt->rp);

So you want the count to get increased for skipped element also?

Thanks,
Mani

> @@ -820,6 +824,9 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>  		enum mhi_pkt_type type = MHI_TRE_GET_EV_TYPE(local_rp);
>  
>  		chan = MHI_TRE_GET_EV_CHID(local_rp);
> +		if (WARN_ON(chan >= mhi_cntrl->max_chan))
> +			goto next_event;
> +
>  		mhi_chan = &mhi_cntrl->mhi_chan[chan];
>  
>  		if (likely(type == MHI_PKT_TYPE_TX_EVENT)) {
> @@ -830,6 +837,7 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>  			event_quota--;
>  		}
>  
> +next_event:
>  		mhi_recycle_ev_ring_element(mhi_cntrl, ev_ring);
>  		local_rp = ev_ring->rp;
>  		dev_rp = mhi_to_virtual(ev_ring, er_ctxt->rp);
> -- 
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>