linux-kernel - [PATCH 06/12] acpi: Limit access to custom_method if trusted

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Date:	Fri, 13 Mar 2015 11:38:22 -1000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-security-module@...r.kernel.org
Cc:	james.l.morris@...cle.com, serge@...lyn.com,
	linux-kernel@...r.kernel.org, keescook@...omium.org, hpa@...or.com,
	gnomes@...rguk.ukuu.org.uk,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 06/12] acpi: Limit access to custom_method if trusted_kernel is true

custom_method effectively allows arbitrary access to system memory, making
it possible for an attacker to modify the kernel at runtime. Prevent this
if trusted_kernel is true.

Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
---
 drivers/acpi/custom_method.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index c68e724..774bb7b 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -8,6 +8,7 @@
 #include <linux/uaccess.h>
 #include <linux/debugfs.h>
 #include <linux/acpi.h>
+#include <linux/security.h>
 
 #include "internal.h"
 
@@ -29,6 +30,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
 	struct acpi_table_header table;
 	acpi_status status;
 
+	if (get_trusted_kernel())
+		return -EPERM;
+
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
 		if (count <= sizeof(struct acpi_table_header))
-- 
2.1.0

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