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Date:   Tue, 30 Jul 2019 15:07:47 +0300
From:   Heikki Krogerus <heikki.krogerus@linux.intel.com>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Douglas Gilbert <dgilbert@interlog.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] usb: typec: tcpm: Ignore unsupported/unknown
 alternate mode requests
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 <20190729140457.GC28600@kuha.fi.intel.com>
 <20190729173104.GA32556@roeck-us.net>
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On Mon, Jul 29, 2019 at 10:31:04AM -0700, Guenter Roeck wrote:
> On Mon, Jul 29, 2019 at 05:04:57PM +0300, Heikki Krogerus wrote:
> > Hi,
> > 
> > On Wed, Jul 24, 2019 at 09:30:37PM -0700, Guenter Roeck wrote:
> > > TCPM may receive PD messages associated with unknown or unsupported
> > > alternate modes. If that happens, calls to typec_match_altmode()
> > > will return NULL. The tcpm code does not currently take this into
> > > account. This results in crashes.
> > > 
> > > Unable to handle kernel NULL pointer dereference at virtual address 000001f0
> > > pgd = 41dad9a1
> > > [000001f0] *pgd=00000000
> > > Internal error: Oops: 5 [#1] THUMB2
> > > Modules linked in: tcpci tcpm
> > > CPU: 0 PID: 2338 Comm: kworker/u2:0 Not tainted 5.1.18-sama5-armv7-r2 #6
> > > Hardware name: Atmel SAMA5
> > > Workqueue: 2-0050 tcpm_pd_rx_handler [tcpm]
> > > PC is at typec_altmode_attention+0x0/0x14
> > > LR is at tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm]
> > > ...
> > > [<c03fbee8>] (typec_altmode_attention) from [<bf8030fb>]
> > > 				(tcpm_pd_rx_handler+0xa3b/0xda0 [tcpm])
> > > [<bf8030fb>] (tcpm_pd_rx_handler [tcpm]) from [<c012082b>]
> > > 				(process_one_work+0x123/0x2a8)
> > > [<c012082b>] (process_one_work) from [<c0120a6d>]
> > > 				(worker_thread+0xbd/0x3b0)
> > > [<c0120a6d>] (worker_thread) from [<c012431f>] (kthread+0xcf/0xf4)
> > > [<c012431f>] (kthread) from [<c01010f9>] (ret_from_fork+0x11/0x38)
> > > 
> > > Ignore PD messages if the asociated alternate mode is not supported.
> > > 
> > > Reported-by: Douglas Gilbert <dgilbert@interlog.com>
> > > Cc: Douglas Gilbert <dgilbert@interlog.com>
> > > Fixes: e9576fe8e605c ("usb: typec: tcpm: Support for Alternate Modes")
> > > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > > ---
> > > Taking a stab at the problem. I don't really know if this is the correct
> > > fix, or even if my understanding of the problem is correct, thus marking
> > > the patch as RFC.
> > 
> > My guess is that typec_match_altmode() is the real culprit. We can't
> > rely on the partner mode index number when identifying the port alt
> > mode.
> > 
> > Douglas, can you test the attached hack instead of this patch?
> > 
> > 
> > thanks,
> > 
> > -- 
> > heikki
> 
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index ec525811a9eb..033dc097ba83 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -1067,12 +1067,11 @@ static int tcpm_pd_svdm(struct tcpm_port *port, const __le32 *payload, int cnt,
> >  
> >  	modep = &port->mode_data;
> >  
> > -	adev = typec_match_altmode(port->port_altmode, ALTMODE_DISCOVERY_MAX,
> > -				   PD_VDO_VID(p[0]), PD_VDO_OPOS(p[0]));
> > -
> >  	pdev = typec_match_altmode(port->partner_altmode, ALTMODE_DISCOVERY_MAX,
> >  				   PD_VDO_VID(p[0]), PD_VDO_OPOS(p[0]));
> >  
> > +	adev = (void *)typec_altmode_get_partner(pdev);
> > +
> 
> I understand that typec_altmode_get_partner() returns a const *;
> maybe adev should be declared as const struct typec_altmode *
> instead of using a typecast.

Yes...

> Also, typec_altmode_get_partner() can return NULL as well if pdev is NULL.
> Is it guaranteed that typec_match_altmode() never returns NULL for pdev ?

...and probable no. But I don't think we can receive Attention to a
mode that hasn't been entered.

I'm not proposing that as a patch. It's just a hunch. That's why I'm
calling it a "hack". Before we prepare anything finalized, I would
like to here from Douglas if he's able to test that or not?


thanks,

-- 
heikki