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Date:   Tue, 26 Mar 2019 11:27:29 -0700
In-Reply-To: <20190326182742.16950-1-matthewgarrett@google.com>
Message-Id: <20190326182742.16950-14-matthewgarrett@google.com>
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References: <20190326182742.16950-1-matthewgarrett@google.com>
Subject: [PATCH V31 13/25] ACPI: Limit access to custom_method when the kernel
 is locked down
From:   Matthew Garrett <matthewgarrett@google.com>
To:     jmorris@namei.org
Cc:     linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, dhowells@redhat.com,
        linux-api@vger.kernel.org, luto@kernel.org,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Matthew Garrett <mjg59@google.com>, linux-acpi@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
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From: Matthew Garrett <mjg59@srcf.ucam.org>

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@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-acpi@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 4451877f83b6..37de3cd84493 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", LOCKDOWN_INTEGRITY))
+		return -EPERM;
+
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
 		if (count <= sizeof(struct acpi_table_header))
-- 
2.21.0.392.gf8f6787159e-goog