[PATCH 12/16] ACPI: Limit access to custom_method when the kernel is locked down

From: David Howells
Date: Wed Nov 16 2016 - 16:48:56 EST

From: Matthew Garrett <matthew.garrett@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>

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..e4d721c330c0 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())
+ return -EPERM;
if (!(*ppos)) {
/* parse the table header to get the table length */
if (count <= sizeof(struct acpi_table_header))