linux-kernel - Re: [RFC][PATCH] drm: i915: do not NULL deref hdmi attached

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Message-ID: <20241113083920.GH1458936@google.com>
Date: Wed, 13 Nov 2024 17:39:20 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] drm: i915: do not NULL deref hdmi attached_connector

On (24/10/31 19:51), Sergey Senozhatsky wrote:
> intel_ddi_init() may skip connector initialization, for instance,
> both intel_ddi_init_dp_connector() and intel_ddi_init_hdmi_connector()
> are optional.  This leads to situation that ->attached_connector may
> be NULL for some connectors.  For instance, on my setup 'DDI A/PHY A'
> and 'DDI TC1/PHY TC1' are not initialized.
> 
> However, functions like intel_dp_dual_mode_set_tmds_output() and
> friends don't take this into consideration.  This leads to NULL
> ptr-derefs:
> 
> KASAN: null-ptr-deref in range [0x0000000000000848-0x000000000000084f]
> RIP: 0010:intel_hdmi_encoder_shutdown+0x105/0x230
> Call Trace:
> <TASK>
> i915_driver_shutdown+0x2d8/0x490
> pci_device_shutdown+0x83/0x150
> device_shutdown+0x4ad/0x660
> __se_sys_reboot+0x29c/0x4d0
> do_syscall_64+0x60/0x90
> 
> Add a new helper to avoid NULL ->attached_connector derefs and
> switch some intel_hdmi function to it.  I'm not sure if we need
> to switch all or just intel_dp_dual_mode_set_tmds_output() (I
> have only seen this one doing NULL derefs so far).

Folks, any more comments / opinions on this?
What should be the way forward?