Re: [PATCH v1 2/8] bus: mhi: core: Add range check for channel id received in event ring

[Hemant Kumar]

On 4/27/20 11:50 AM, Jeffrey Hugo wrote:
> On 4/27/2020 12:32 PM, 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>
>
> I believe your SOB is needed here after Hemant's per section 11 of 
> Documentation/process/submitting-patches.rst
>
> > ---
> > Â drivers/bus/mhi/core/main.c | 3 +++
> > Â 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> > index 23154f1..ba8afa7 100644
> > --- a/drivers/bus/mhi/core/main.c
> > +++ b/drivers/bus/mhi/core/main.c
> > @@ -827,6 +827,9 @@ int mhi_process_data_event_ring(struct 
> > mhi_controller *mhi_cntrl,
> > ÂÂÂÂÂÂÂÂÂ enum mhi_pkt_type type = MHI_TRE_GET_EV_TYPE(local_rp);
> > ÂÂÂÂÂÂÂÂÂ chan = MHI_TRE_GET_EV_CHID(local_rp);
> > +ÂÂÂÂÂÂÂ if (WARN_ON(chan >= mhi_cntrl->max_chan))
> > +ÂÂÂÂÂÂÂÂÂÂÂ continue;
> > +
> > ÂÂÂÂÂÂÂÂÂ mhi_chan = &mhi_cntrl->mhi_chan[chan];
> > ÂÂÂÂÂÂÂÂÂ if (likely(type == MHI_PKT_TYPE_TX_EVENT)) {
>
> How does this work?
>
> I understand the need for the range check, however I looks like this 
> change doesn't do proper handling.
>
> Since all you do is "continue", we'll remain stuck in the while loop 
> this exists in, continuously "processing" the same event, failing the 
> same check, and spamming the kernel log with the WARN_ON output until 
> the end of time.
>
> What am I missing?
Idea was to drop the event and continue, but continue statement is 
wrong here, we need to recycle the event and continue after that. Will 
fix in V2.
> What is the behavior you want? Do you want to just drop/ignore the 
> invalid event, or issue a reset of the device because it is clearly 
> misbehaving?

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