[PATCH 05/12] Restrict /dev/mem and /dev/kmem when securelevel is set.

Matthew Garrett
2013-09-09T15:52:28Z

Allowing users to write to address space provides mechanisms that may permit
modification of the kernel at runtime. Prevent this if securelevel has been
set.

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 741f536..91d1cff 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 (get_securelevel() > 0)
+ 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 (get_securelevel() > 0)
+ 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