[PATCH 05/24] Restrict /dev/mem and /dev/kmem when the kernel is locked down

[David Howells]

From: Matthew Garrett <matthew.garr...@nebula.com>

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.garr...@nebula.com>
Signed-off-by: David Howells <dhowe...@redhat.com>
---

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

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 6d9cc2d39d22..f8144049bda3 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -163,6 +163,9 @@ 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;
 
@@ -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 (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);