linux-kernel - Re: [PATCH] cxl/acpi: Add Null check for adev

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Message-ID: <Z9NWdob3CSy9UDq5@aschofie-mobl2.lan>
Date: Thu, 13 Mar 2025 15:04:38 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Chenyuan Yang <chenyuan0y@...il.com>
Cc: dave@...olabs.net, jonathan.cameron@...wei.com, dave.jiang@...el.com,
	vishal.l.verma@...el.com, ira.weiny@...el.com,
	dan.j.williams@...el.com, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cxl/acpi: Add Null check for adev

On Thu, Mar 13, 2025 at 02:07:53PM -0500, Chenyuan Yang wrote:
> Not all devices have an ACPI companion fwnode, so adev might be NULL.
> This is similar to the commit cd2fd6eab480
> ("platform/x86: int3472: Check for adev == NULL").
> 
> Add a check for adev not being set and return -ENODEV in that case to
> avoid a possible NULL pointer deref in cxl_acpi_probe().
> 

Avoiding the NULL ptr deref seems obvious as ACPI_COMPANION() return
is routinely checked throughout the kernel. Why the reference to the
other commit? Do these devices have something in common?

I'm curious as to when *this* specific adev can be NULL.

Looks good to check it like you do here, or if someone chimes in that
it can never be NULL, just add a code comment saying so.

Perhaps emit a message on NULL too.



> Signed-off-by: Chenyuan Yang <chenyuan0y@...il.com>
> ---
>  drivers/cxl/acpi.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index cb14829bb9be..9195001db3c1 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -823,6 +823,9 @@ static int cxl_acpi_probe(struct platform_device *pdev)
>  	struct acpi_device *adev = ACPI_COMPANION(host);
>  	struct cxl_cfmws_context ctx;
>  
> +	if (!adev)
> +		return -ENODEV;
> +
>  	device_lock_set_class(&pdev->dev, &cxl_root_key);
>  	rc = devm_add_action_or_reset(&pdev->dev, cxl_acpi_lock_reset_class,
>  				      &pdev->dev);
> -- 
> 2.34.1
>