linux-kernel - Re: [RFC PATCH] usb: typec: tcpm: Ignore unsupported/unknown alternate mode requests

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Date:   Mon, 29 Jul 2019 17:04:57 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Douglas Gilbert <dgilbert@...erlog.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] usb: typec: tcpm: Ignore unsupported/unknown
 alternate mode requests

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@...erlog.com>
> Cc: Douglas Gilbert <dgilbert@...erlog.com>
> Fixes: e9576fe8e605c ("usb: typec: tcpm: Support for Alternate Modes")
> Signed-off-by: Guenter Roeck <linux@...ck-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

View attachment "tcpm_hack.diff" of type "text/plain" (677 bytes)