ACPI: Limit access to custom_method when the kernel is locked down

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 <mjg59@srcf.ucam.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
cc: linux-acpi@vger.kernel.org

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0015-ACPI-Limit-access-to-custom_method-when-the-kernel-i.patch

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index b2ef4c2ec955d5c737a69aac1cde444dcd351caf..33b821be0600a102cd5f87a2a4f0c659d39763d1 100644 (file)
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -30,6 +30,9 @@ 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))