Restrict /dev/mem and /dev/kmem when the kernel is locked down

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@nebula.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0042-Restrict-dev-mem-and-dev-kmem-when-the-kernel-is-loc.patch

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 593a8818aca99e345e03d0fb56eabd25b5ffd05a..ba68add9677f43c2994e1e5c589e18d1d075da92 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -179,6 +179,9 @@ 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;
 
@@ -540,6 +543,9 @@ 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);