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

Manivannan Sadhasivam
2020-05-08T05:45:28Z

On Tue, May 05, 2020 at 03:47:07PM -0700, Bhaumik Bhatt wrote:
> From: Hemant Kumar <hemantk@codeaurora.org>
>
> 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@codeaurora.org>
> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
> Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
> ---
> 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);
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>