6 files changed, 109 insertions, 11 deletions
diff --git a/security/Kconfig b/security/Kconfig
index d23c839038f..4c865345caa 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -113,6 +113,22 @@ config SECURITY_ROOTPLUG
 
 	  If you are unsure how to answer this question, answer N.
 
+config LSM_MMAP_MIN_ADDR
+	int "Low address space for LSM to protect from user allocation"
+	depends on SECURITY && SECURITY_SELINUX
+	default 65536
+	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 c67557cdaa8..b56e7f9ecbc 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -8,7 +8,7 @@ subdir-$(CONFIG_SECURITY_SMACK)		+= smack
 subdir-$(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/capability.c b/security/capability.c
index 21b6cead6a8..88f752e8152 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -330,15 +330,6 @@ static int cap_file_ioctl(struct file *file, unsigned int command,
 	return 0;
 }
 
-static int cap_file_mmap(struct file *file, unsigned long reqprot,
-			 unsigned long prot, unsigned long flags,
-			 unsigned long addr, unsigned long addr_only)
-{
-	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
-		return -EACCES;
-	return 0;
-}
-
 static int cap_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
 			     unsigned long prot)
 {
diff --git a/security/commoncap.c b/security/commoncap.c
index 48b7e0228fa..e3097c0a131 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -984,3 +984,33 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
 		cap_sys_admin = 1;
 	return __vm_enough_memory(mm, pages, cap_sys_admin);
 }
+
+/*
+ * cap_file_mmap - check if able to map given addr
+ * @file: unused
+ * @reqprot: unused
+ * @prot: unused
+ * @flags: unused
+ * @addr: address attempting to be mapped
+ * @addr_only: unused
+ *
+ * If the process is attempting to map memory below mmap_min_addr they need
+ * CAP_SYS_RAWIO.  The other parameters to this function are unused by the
+ * capability security module.  Returns 0 if this mapping should be allowed
+ * -EPERM if not.
+ */
+int cap_file_mmap(struct file *file, unsigned long reqprot,
+		  unsigned long prot, unsigned long flags,
+		  unsigned long addr, unsigned long addr_only)
+{
+	int ret = 0;
+
+	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 */
+		if (ret == 0)
+			current->flags |= PF_SUPERPRIV;
+	}
+	return ret;
+}
diff --git a/security/min_addr.c b/security/min_addr.c
new file mode 100644
index 00000000000..14cc7b3b8d0
--- /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 1e8cfc4c2ed..8d8b69c5664 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3030,9 +3030,21 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
 	int rc = 0;
 	u32 sid = current_sid();
 
-	if (addr < mmap_min_addr)
+	/*
+	 * notice that we are intentionally putting the SELinux check before
+	 * the secondary cap_file_mmap check.  This is such a likely attempt
+	 * at bad behaviour/exploit that we always want to get the AVC, even
+	 * if DAC would have also denied the operation.
+	 */
+	if (addr < CONFIG_LSM_MMAP_MIN_ADDR) {
 		rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
 				  MEMPROTECT__MMAP_ZERO, NULL);
+		if (rc)
+			return rc;
+	}
+
+	/* do DAC check on address space usage */
+	rc = cap_file_mmap(file, reqprot, prot, flags, addr, addr_only);
 	if (rc || addr_only)
 		return rc;