Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE_PTR to point at unmapped space)

Christoph Lameter
2009-06-03T19:00:00Z

We could just move the check for mmap_min_addr out from
CONFIG_SECURITY?

Use mmap_min_addr indepedently of security models

This patch removes the dependency of mmap_min_addr on CONFIG_SECURITY.
It also sets a default mmap_min_addr of 4096.

mmapping of addresses below 4096 will only be possible for processes
with CAP_SYS_RAWIO.

Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

---
include/linux/mm.h | 2 --
kernel/sysctl.c | 2 --
mm/Kconfig | 19 +++++++++++++++++++
mm/mmap.c | 6 ++++++
security/Kconfig | 20 --------------------
security/capability.c | 2 --
security/security.c | 3 ---
7 files changed, 25 insertions(+), 29 deletions(-)

Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/include/linux/mm.h 2009-06-03 13:48:10.000000000 -0500
@@ -580,12 +580,10 @@ static inline void set_page_links(struct
*/
static inline unsigned long round_hint_to_min(unsigned long hint)
{
-#ifdef CONFIG_SECURITY
hint &= PAGE_MASK;
if (((void *)hint != NULL) &&
(hint < mmap_min_addr))
return PAGE_ALIGN(mmap_min_addr);
-#endif
return hint;
}

Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/kernel/sysctl.c 2009-06-03 13:48:10.000000000 -0500
@@ -1225,7 +1225,6 @@ static struct ctl_table vm_table[] = {
.strategy = &sysctl_jiffies,
},
#endif
-#ifdef CONFIG_SECURITY
{
.ctl_name = CTL_UNNUMBERED,
.procname = "mmap_min_addr",
@@ -1234,7 +1233,6 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = &proc_doulongvec_minmax,
},
-#endif
#ifdef CONFIG_NUMA
{
.ctl_name = CTL_UNNUMBERED,
Index: linux-2.6/mm/mmap.c
===================================================================
--- linux-2.6.orig/mm/mmap.c 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/mm/mmap.c 2009-06-03 13:48:10.000000000 -0500
@@ -87,6 +87,9 @@ int sysctl_overcommit_ratio = 50; /* def
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
@@ -1043,6 +1046,9 @@ unsigned long do_mmap_pgoff(struct file
}
}

+ if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ return -EACCES;
+
error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
if (error)
return error;
Index: linux-2.6/security/security.c
===================================================================
--- linux-2.6.orig/security/security.c 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/security/security.c 2009-06-03 13:48:10.000000000 -0500
@@ -26,9 +26,6 @@ extern void security_fixup_ops(struct se

struct security_operations *security_ops; /* Initialized to NULL */

-/* 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)
{
/* verify the security_operations structure exists */
Index: linux-2.6/mm/Kconfig
===================================================================
--- linux-2.6.orig/mm/Kconfig 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/mm/Kconfig 2009-06-03 13:48:10.000000000 -0500
@@ -226,6 +226,25 @@ config HAVE_MLOCKED_PAGE_BIT
config MMU_NOTIFIER
bool

+config DEFAULT_MMAP_MIN_ADDR
+ int "Low address space to protect from user allocation"
+ default 4096
+ 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 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.
+
+
config NOMMU_INITIAL_TRIM_EXCESS
int "Turn on mmap() excess space trimming before booting"
depends on !MMU
Index: linux-2.6/security/Kconfig
===================================================================
--- linux-2.6.orig/security/Kconfig 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/security/Kconfig 2009-06-03 13:48:10.000000000 -0500
@@ -113,26 +113,6 @@ config SECURITY_ROOTPLUG

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 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.
-
- This value can be changed after boot using the
- /proc/sys/vm/mmap_min_addr tunable.
-
-
source security/selinux/Kconfig
source security/smack/Kconfig
source security/tomoyo/Kconfig
Index: linux-2.6/security/capability.c
===================================================================
--- linux-2.6.orig/security/capability.c 2009-06-03 13:48:01.000000000 -0500
+++ linux-2.6/security/capability.c 2009-06-03 13:48:10.000000000 -0500
@@ -334,8 +334,6 @@ static int cap_file_mmap(struct file *fi
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;
}