linux-kernel - [PATCH 06/10] Restrict /dev/mem and /dev/kmem when module loading is restricted

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Message-Id: <1376928619-3775-6-git-send-email-matthew.garrett@nebula.com>
Date:	Mon, 19 Aug 2013 12:10:15 -0400
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-efi@...r.kernel.org, jwboyer@...hat.com,
	keescook@...omium.org, Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 06/10] Restrict /dev/mem and /dev/kmem when module loading is restricted

Allowing users to write to address space makes it possible for the kernel
to be subverted, avoiding module loading restrictions. Prevent this when
any restrictions have been imposed on loading modules.

Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
---
 drivers/char/mem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 1af8664..61406c8 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -159,6 +159,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 	unsigned long copied;
 	void *ptr;
 
+	if (secure_modules())
+		return -EPERM;
+
 	if (!valid_phys_addr_range(p, count))
 		return -EFAULT;
 
@@ -497,6 +500,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
 	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
 	int err = 0;
 
+	if (secure_modules())
+		return -EPERM;
+
 	if (p < (unsigned long) high_memory) {
 		unsigned long to_write = min_t(unsigned long, count,
 					       (unsigned long)high_memory - p);
-- 
1.8.3.1

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