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From: Matthew Garrett <matthew.garrett@nebula.com>
Date: Fri, 9 Mar 2012 09:28:15 -0500
Subject: [PATCH] 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@nebula.com>
---
 drivers/char/mem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index efe38c1bc234..16b8af1188e1 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -167,6 +167,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 	if (p != *ppos)
 		return -EFBIG;
 
+	if (secure_modules())
+		return -EPERM;
+
 	if (!valid_phys_addr_range(p, count))
 		return -EFAULT;
 
@@ -513,6 +516,9 @@ 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);