Re: [PATCH] bus: mhi: ep: Fix off by one in mhi_ep_process_cmd_ring()

[Manivannan Sadhasivam <mani@kernel.org>]

On Thu, Jan 26, 2023 at 07:26:32AM -0600, Alex Elder wrote:
> On 1/26/23 3:29 AM, Dan Carpenter wrote:
> > The > comparison should be changed to >= to prevent an out of bounds
> > access into the mhi_cntrl->mhi_chan[] array.  The mhi_cntrl->mhi_chan[]
> > array is allocated in mhi_ep_chan_init() and has mhi_cntrl->max_chan
> > elements.
> 
> You're right.  I scanned through that file and there
> are other spots that don't check that the channel ID
> is in range, though I think this is the one where it's
> reading it from an external source.  I.e., the other
> places are aleady known to be correct.  (Maybe Mani
> can comment.)
> 

Right. This is the only place we get the channel id from the host, so that's
why the check is needed only here.

> Reviewed-by: Alex Elder <elder@linaro.org>

Thanks,
Mani

> 
> > 
> > Fixes: 2527ad44ddb2 ("bus: mhi: ep: Check if the channel is supported by the controller")
> > Signed-off-by: Dan Carpenter <error27@gmail.com>
> > ---
> >   drivers/bus/mhi/ep/main.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> > index bcaaba97ef63..be2d56e7f392 100644
> > --- a/drivers/bus/mhi/ep/main.c
> > +++ b/drivers/bus/mhi/ep/main.c
> > @@ -125,7 +125,7 @@ static int mhi_ep_process_cmd_ring(struct mhi_ep_ring *ring, struct mhi_ring_ele
> >   	ch_id = MHI_TRE_GET_CMD_CHID(el);
> >   	/* Check if the channel is supported by the controller */
> > -	if ((ch_id > mhi_cntrl->max_chan) || !mhi_cntrl->mhi_chan[ch_id].name) {
> > +	if ((ch_id >= mhi_cntrl->max_chan) || !mhi_cntrl->mhi_chan[ch_id].name) {
> >   		dev_err(dev, "Channel (%u) not supported!\n", ch_id);
> >   		return -ENODEV;
> >   	}
> 

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