[PATCH 14/27] ACPI: Limit access to custom_method when the kernel is locked down

[joeyli]

On Thu, Oct 19, 2017 at 03:52:19PM +0100, David Howells wrote:
> From: Matthew Garrett <matthew.garrett at nebula.com>
> 
> custom_method effectively allows arbitrary access to system memory, making
> it possible for an attacker to circumvent restrictions on module loading.
> Disable it if the kernel is locked down.
> 
> Signed-off-by: Matthew Garrett <matthew.garrett at nebula.com>
> Signed-off-by: David Howells <dhowells at redhat.com>

I have reviewed this patch. Please feel free to add:

Reviewed-by: "Lee, Chun-Yi" <jlee at suse.com>

Thanks!
Joey Lee

> cc: linux-acpi at vger.kernel.org
> ---
> 
>  drivers/acpi/custom_method.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
> index c68e72414a67..b33fba70ec51 100644
> --- a/drivers/acpi/custom_method.c
> +++ b/drivers/acpi/custom_method.c
> @@ -29,6 +29,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
>  	struct acpi_table_header table;
>  	acpi_status status;
>  
> +	if (kernel_is_locked_down("ACPI custom methods"))
> +		return -EPERM;
> +
>  	if (!(*ppos)) {
>  		/* parse the table header to get the table length */
>  		if (count <= sizeof(struct acpi_table_header))
> 
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