[PATCH 14/16] Restrict /dev/mem and /dev/kmem when the kernel is locked down

[David Howells]

From: Matthew Garrett <matthew.garrett@xxxxxxxxxx>

Allowing users to write to address space makes it possible for the kernel to
be subverted, avoiding module loading restrictions.  Prevent this when the
kernel has been locked down.

Signed-off-by: Matthew Garrett <matthew.garrett@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 drivers/char/mem.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 17e22cb2db14..5dcc205e8373 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -164,6 +164,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 	if (p != *ppos)
 		return -EFBIG;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	if (!valid_phys_addr_range(p, count))
 		return -EFAULT;
 
@@ -516,6 +519,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
 	if (!pfn_valid(PFN_DOWN(p)))
 		return -EIO;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	if (p < (unsigned long) high_memory) {
 		unsigned long to_write = min_t(unsigned long, count,
 					       (unsigned long)high_memory - p);