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From: Jameson Thies <jthies@google.com>
Date: Thu, 2 May 2024 15:47:41 -0700
Message-ID: <CAMFSARc7GPZuvX1wbyvz2uPUeORObuw3=JQ1QwKYRenaofXvBQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] usb: typec: ucsi: Fix null deref in trace
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: heikki.krogerus@linux.intel.com, linux-usb@vger.kernel.org, 
	pmalani@chromium.org, bleung@google.com, abhishekpandit@chromium.org, 
	andersson@kernel.org, dmitry.baryshkov@linaro.org, 
	fabrice.gasnier@foss.st.com, gregkh@linuxfoundation.org, hdegoede@redhat.com, 
	neil.armstrong@linaro.org, rajaram.regupathy@intel.com, 
	saranya.gopal@intel.com, linux-kernel@vger.kernel.org
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Hi Dan,
thank you for the reference. In this case I think returning NULL from
ucsi_register_displayport stub and using a NULL check to prevent a
NULL pointer dereference won't give us the desired behavior. When
CONFIG_TYPEC_DP_ALTMODE is not enabled, the function would return NULL
and the UCSI driver will never end up registering DisplayPort
alternate mode. I'll update the commit message to note that this patch
adds a fallback registration for DisplayPort alternate mode in
addition to simply fixing the NULL pointer dereference caused by
returning it in the ucsi_register_displayport stub. Separately we
could add a NULL check, but I don't think it's necessary. Neither the
non-stub ucsi_register_displayport or typec_port_register_altmode look
like they will return NULL.

Thanks,
Jameson