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>
diff --git a/security/Kconfig b/security/Kconfig
index 25ffe1b..5dfc206 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -104,6 +104,24 @@
If you are unsure how to answer this question, answer N.
+config SECURITY_DEFAULT_MMAP_MIN_ADDR
+ int "Low address space to protect from user allocation"
+ depends on SECURITY
+ default 0
+ help
+ This is the portion of low virtual memory which should be protected
+ from userspace allocation. Keeping a user from writing to low pages
+ can help reduce the impact of kernel NULL pointer bugs.
+
+ For most users with lots of address space a value of 65536 is
+ reasonable and should cause no problems. Programs which use vm86
+ functionality would either need additional permissions from either
+ the LSM or the capabilities module or have this protection disabled.
+
+ This value can be changed after boot using the
+ /proc/sys/vm/mmap_min_addr tunable.
+
+
source security/selinux/Kconfig
source security/smack/Kconfig