Re: [PATCH 1/8] bus: mhi: core: Validate channel ID when processing command completions

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jun 21, 2021 at 09:46:09PM +0530, Manivannan Sadhasivam wrote:
> From: Bhaumik Bhatt <bbhatt@codeaurora.org>
> 
> MHI reads the channel ID from the event ring element sent by the
> device which can be any value between 0 and 255. In order to
> prevent any out of bound accesses, add a check against the maximum
> number of channels supported by the controller and those channels
> not configured yet so as to skip processing of that event ring
> element.
> 
> Cc: stable@vger.kernel.org
> Fixes: 1d3173a3bae7 ("bus: mhi: core: Add support for processing events from client device")
> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
> Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
> Link: https://lore.kernel.org/r/1619481538-4435-1-git-send-email-bbhatt@codeaurora.org
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/bus/mhi/core/main.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 22acde118bc3..ed07421c4870 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -773,11 +773,16 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
>  	cmd_pkt = mhi_to_virtual(mhi_ring, ptr);
>  
>  	chan = MHI_TRE_GET_CMD_CHID(cmd_pkt);
> -	mhi_chan = &mhi_cntrl->mhi_chan[chan];
> -	write_lock_bh(&mhi_chan->lock);
> -	mhi_chan->ccs = MHI_TRE_GET_EV_CODE(tre);
> -	complete(&mhi_chan->completion);
> -	write_unlock_bh(&mhi_chan->lock);
> +	WARN_ON(chan >= mhi_cntrl->max_chan);

What can ever trigger this WARN_ON()?  Do you mean to reboot a machine
if panic-on-warn is set?

If this can actually happen, then check for it and recover properly,
don't just blindly warn and then keep on going.

thanks,

greg k-h