security: allow Kconfig to set default mmap_min_addr protection

Since it was decided that low memory protection from userspace couldn't
be turned on by default add a Kconfig option to allow users/distros to
set a default at compile time.  This value is still tunable after boot
in /proc/sys/vm/mmap_min_addr

Discussion:
http://www.mail-archive.com/linux-security-module@vger.kernel.org/msg02543.html

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/security/security.c b/security/security.c
index b6c57a6b2ff5..d15e56cbaade 100644
--- a/security/security.c
+++ b/security/security.c
@@ -23,7 +23,9 @@ extern struct security_operations dummy_security_ops;
 extern void security_fixup_ops(struct security_operations *ops);
 
 struct security_operations *security_ops;       /* Initialized to NULL */
-unsigned long mmap_min_addr;            /* 0 means no protection */
+
+/* amount of vm to protect from userspace access */
+unsigned long mmap_min_addr = CONFIG_SECURITY_DEFAULT_MMAP_MIN_ADDR;
 
 static inline int verify(struct security_operations *ops)
 {