Security/SELinux: seperate lsm specific mmap_min_addr
Currently SELinux enforcement of controls on the ability to map low memory
is determined by the mmap_min_addr tunable. This patch causes SELinux to
ignore the tunable and instead use a seperate Kconfig option specific to how
much space the LSM should protect.
The tunable will now only control the need for CAP_SYS_RAWIO and SELinux
permissions will always protect the amount of low memory designated by
CONFIG_LSM_MMAP_MIN_ADDR.
This allows users who need to disable the mmap_min_addr controls (usual reason
being they run WINE as a non-root user) to do so and still have SELinux
controls preventing confined domains (like a web server) from being able to
map some area of low memory.
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 d23c839..9c60c34 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -113,6 +113,22 @@
If you are unsure how to answer this question, answer N.
+config LSM_MMAP_MIN_ADDR
+ int "Low address space for LSM to from user allocation"
+ depends on SECURITY && SECURITY_SELINUX
+ default 65535
+ 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 ia64, ppc64 and x86 users with lots of address space
+ a value of 65536 is reasonable and should cause no problems.
+ On arm and other archs it should not be higher than 32768.
+ Programs which use vm86 functionality or have some need to map
+ this low address space will need the permission specific to the
+ systems running LSM.
+
source security/selinux/Kconfig
source security/smack/Kconfig
source security/tomoyo/Kconfig
diff --git a/security/Makefile b/security/Makefile
index c67557c..b56e7f9 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -8,7 +8,7 @@
subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo
# always enable default capabilities
-obj-y += commoncap.o
+obj-y += commoncap.o min_addr.o
# Object file lists
obj-$(CONFIG_SECURITY) += security.o capability.o
diff --git a/security/commoncap.c b/security/commoncap.c
index 6bcf6e8..e3097c0 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1005,7 +1005,7 @@
{
int ret = 0;
- if (addr < mmap_min_addr) {
+ if (addr < dac_mmap_min_addr) {
ret = cap_capable(current, current_cred(), CAP_SYS_RAWIO,
SECURITY_CAP_AUDIT);
/* set PF_SUPERPRIV if it turns out we allow the low mmap */
diff --git a/security/min_addr.c b/security/min_addr.c
new file mode 100644
index 0000000..14cc7b3
--- /dev/null
+++ b/security/min_addr.c
@@ -0,0 +1,49 @@
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/security.h>
+#include <linux/sysctl.h>
+
+/* amount of vm to protect from userspace access by both DAC and the LSM*/
+unsigned long mmap_min_addr;
+/* amount of vm to protect from userspace using CAP_SYS_RAWIO (DAC) */
+unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
+/* amount of vm to protect from userspace using the LSM = CONFIG_LSM_MMAP_MIN_ADDR */
+
+/*
+ * Update mmap_min_addr = max(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR)
+ */
+static void update_mmap_min_addr(void)
+{
+#ifdef CONFIG_LSM_MMAP_MIN_ADDR
+ if (dac_mmap_min_addr > CONFIG_LSM_MMAP_MIN_ADDR)
+ mmap_min_addr = dac_mmap_min_addr;
+ else
+ mmap_min_addr = CONFIG_LSM_MMAP_MIN_ADDR;
+#else
+ mmap_min_addr = dac_mmap_min_addr;
+#endif
+}
+
+/*
+ * sysctl handler which just sets dac_mmap_min_addr = the new value and then
+ * calls update_mmap_min_addr() so non MAP_FIXED hints get rounded properly
+ */
+int mmap_min_addr_handler(struct ctl_table *table, int write, struct file *filp,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
+
+ update_mmap_min_addr();
+
+ return ret;
+}
+
+int __init init_mmap_min_addr(void)
+{
+ update_mmap_min_addr();
+
+ return 0;
+}
+pure_initcall(init_mmap_min_addr);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e6d1432..8d8b69c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3036,7 +3036,7 @@
* at bad behaviour/exploit that we always want to get the AVC, even
* if DAC would have also denied the operation.
*/
- if (addr < mmap_min_addr) {
+ if (addr < CONFIG_LSM_MMAP_MIN_ADDR) {
rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
MEMPROTECT__MMAP_ZERO, NULL);
if (rc)