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/include/linux/mm.h b/include/linux/mm.h
index ba3a7cb..9a72cc7 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -34,8 +34,6 @@ extern int sysctl_legacy_va_layout;
 #define sysctl_legacy_va_layout 0
 #endif
 
-extern unsigned long mmap_min_addr;
-
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>
@@ -575,19 +573,6 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
 }
 
 /*
- * If a hint addr is less than mmap_min_addr change hint to be as
- * low as possible but still greater than mmap_min_addr
- */
-static inline unsigned long round_hint_to_min(unsigned long hint)
-{
-       hint &= PAGE_MASK;
-       if (((void *)hint != NULL) &&
-           (hint < mmap_min_addr))
-               return PAGE_ALIGN(mmap_min_addr);
-       return hint;
-}
-
-/*
  * Some inline functions in vmstat.h depend on page_zone()
  */
 #include <linux/vmstat.h>

diff --git a/include/linux/security.h b/include/linux/security.h
index 963a48f..7b43115 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -28,6 +28,7 @@
 #include <linux/resource.h>
 #include <linux/sem.h>
 #include <linux/shm.h>
+#include <linux/mm.h> /* PAGE_ALIGN */
 #include <linux/msg.h>
 #include <linux/sched.h>
 #include <linux/key.h>
@@ -95,6 +96,7 @@ extern int cap_netlink_send(struct sock *sk, struct sk_buff *skb);
 extern int cap_netlink_recv(struct sk_buff *skb, int cap);
 
 extern unsigned long mmap_min_addr;
+extern unsigned long dac_mmap_min_addr;
 /*
  * Values used in the task_security_ops calls
  */
@@ -147,6 +149,21 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
        opts->num_mnt_opts = 0;
 }
 
+/*
+ * If a hint addr is less than mmap_min_addr change hint to be as
+ * low as possible but still greater than mmap_min_addr
+ */
+static inline unsigned long round_hint_to_min(unsigned long hint)
+{
+       hint &= PAGE_MASK;
+       if (((void *)hint != NULL) &&
+           (hint < mmap_min_addr))
+               return PAGE_ALIGN(mmap_min_addr);
+       return hint;
+}
+
+extern int mmap_min_addr_handler(struct ctl_table *table, int write, struct file *filp,
+                                void __user *buffer, size_t *lenp, loff_t *ppos);
 /**
  * struct security_operations - main security structure
  *

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 98e0232..58be760 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -49,6 +49,7 @@
 #include <linux/acpi.h>
 #include <linux/reboot.h>
 #include <linux/ftrace.h>
+#include <linux/security.h>
 #include <linux/slow-work.h>
 #include <linux/perf_counter.h>
 
@@ -1306,10 +1307,10 @@ static struct ctl_table vm_table[] = {
        {
                .ctl_name       = CTL_UNNUMBERED,
                .procname       = "mmap_min_addr",
-               .data           = &mmap_min_addr,
-               .maxlen         = sizeof(unsigned long),
+               .data           = &dac_mmap_min_addr,
+               .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
-               .proc_handler   = &proc_doulongvec_minmax,
+               .proc_handler   = &mmap_min_addr_handler,
        },
 #ifdef CONFIG_NUMA
        {

diff --git a/mm/Kconfig b/mm/Kconfig
index c948d4c..fe5f674 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -225,9 +225,9 @@ config DEFAULT_MMAP_MIN_ADDR
          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 would either need additional
-         permissions from either the LSM or the capabilities module or have
-         this protection disabled.
+         Programs which use vm86 functionality or have some need to map
+         this low address space will need CAP_SYS_RAWIO or disable this
+         protection by setting the value to 0.
 
          This value can be changed after boot using the
          /proc/sys/vm/mmap_min_addr tunable.

diff --git a/mm/mmap.c b/mm/mmap.c
index 34579b2..8101de4 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -88,9 +88,6 @@ int sysctl_overcommit_ratio = 50;     /* default is 50% */
 int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
 struct percpu_counter vm_committed_as;
 
-/* amount of vm to protect from userspace access */
-unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
-
 /*
  * Check that a process has enough memory to allocate a new virtual
  * mapping. 0 means there is enough memory for the allocation to

diff --git a/mm/nommu.c b/mm/nommu.c
index 53cab10..28754c4 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -69,9 +69,6 @@ int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
 int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
 int heap_stack_gap = 0;
 
-/* amount of vm to protect from userspace access */
-unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
-
 atomic_long_t mmap_pages_allocated;
 
 EXPORT_SYMBOL(mem_map);

diff --git a/security/Kconfig b/security/Kconfig
index d23c839..9c60c34 100644 (file)
--- 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 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 (file)
--- 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/commoncap.c b/security/commoncap.c
index 3852e94..fe30751 100644 (file)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1005,7 +1005,7 @@ int cap_file_mmap(struct file *file, unsigned long reqprot,
 {
        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 (file)
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 8a78f58..5dee883 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3040,7 +3040,7 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
         * 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)