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Subject[PATCH -v2 2/2] Security/SELinux: seperate lsm specific mmap_min_addr
Date
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
DEFAULT_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>
---
include/linux/mm.h | 3 +++
include/linux/security.h | 1 -
kernel/sysctl.c | 4 ++--
mm/Kconfig | 6 +++---
mm/Makefile | 2 +-
mm/min_addr.c | 39 +++++++++++++++++++++++++++++++++++++++
mm/mmap.c | 9 +++------
mm/mremap.c | 4 ++--
mm/nommu.c | 5 +----
security/Kconfig | 16 ++++++++++++++++
security/selinux/hooks.c | 2 +-
11 files changed, 71 insertions(+), 20 deletions(-)
create mode 100644 mm/min_addr.c
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ba3a7cb..dc7276a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -35,6 +35,7 @@ extern int sysctl_legacy_va_layout;
#endif

extern unsigned long mmap_min_addr;
+extern unsigned long dac_mmap_min_addr;

#include <asm/page.h>
#include <asm/pgtable.h>
@@ -587,6 +588,8 @@ static inline unsigned long round_hint_to_min(unsigned long hint)
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);
/*
* Some inline functions in vmstat.h depend on page_zone()
*/
diff --git a/include/linux/security.h b/include/linux/security.h
index f7d198a..de774f7 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -91,7 +91,6 @@ struct seq_file;
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;
/*
* Values used in the task_security_ops calls
*/
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 98e0232..b77a74a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1306,10 +1306,10 @@ static struct ctl_table vm_table[] = {
{
.ctl_name = CTL_UNNUMBERED,
.procname = "mmap_min_addr",
- .data = &mmap_min_addr,
+ .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
--- 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/Makefile b/mm/Makefile
index b2b96c2..a06a655 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -11,7 +11,7 @@ obj-y := bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
maccess.o page_alloc.o page-writeback.o \
readahead.o swap.o truncate.o vmscan.o shmem.o \
prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
- page_isolation.o mm_init.o $(mmu-y)
+ page_isolation.o mm_init.o min_addr.o $(mmu-y)
obj-y += init-mm.o

obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
diff --git a/mm/min_addr.c b/mm/min_addr.c
new file mode 100644
index 0000000..d035b7e
--- /dev/null
+++ b/mm/min_addr.c
@@ -0,0 +1,39 @@
+#include <linux/init.h>
+#include <linux/sysctl.h>
+
+/* amount of vm to protect from userspace access */
+unsigned long mmap_min_addr;
+/* amount of vm to protect from userspace using CAP_SYS_RAWIO */
+unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
+
+static void update_mmap_min_addr(void)
+{
+#ifdef CONFIG_SECURITY
+ if (dac_mmap_min_addr > CONFIG_DEFAULT_LSM_MMAP_MIN_ADDR)
+ mmap_min_addr = dac_mmap_min_addr;
+ else
+ dac_mmap_min_addr = CONFIG_DEFAULT_LSM_MMAP_MIN_ADDR;
+#else
+ mmap_min_addr = dac_mmap_min_addr;
+#endif
+}
+
+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/mm/mmap.c b/mm/mmap.c
index 3bc88c4..0782eb2 100644
--- 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
@@ -1051,7 +1048,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
if (error)
return error;

- if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((addr < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
return -EACCES;

error = ima_file_mmap(file, prot);
@@ -1666,7 +1663,7 @@ static int expand_downwards(struct vm_area_struct *vma,
if (error)
return error;

- if ((address < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((address < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
return -EACCES;

anon_vma_lock(vma);
@@ -2010,7 +2007,7 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
if (error)
return error;

- if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((addr < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
return -EACCES;

flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
diff --git a/mm/mremap.c b/mm/mremap.c
index fc866c3..099efab 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -304,7 +304,7 @@ unsigned long do_mremap(unsigned long addr,
goto out;

ret = -EACCES;
- if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((new_addr < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
goto out;

ret = do_munmap(mm, new_addr, new_len);
@@ -416,7 +416,7 @@ unsigned long do_mremap(unsigned long addr,
goto out;

ret = -EACCES;
- if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((new_addr < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
goto out;
}
ret = move_vma(vma, addr, old_len, new_len, new_addr);
diff --git a/mm/nommu.c b/mm/nommu.c
index 891ed70..f239940 100644
--- 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);
@@ -999,7 +996,7 @@ static int validate_mmap_request(struct file *file,
if (ret < 0)
return ret;

- if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ if ((addr < dac_mmap_min_addr) && !capable(CAP_SYS_RAWIO))
return -EACCES;

/* looks okay */
diff --git a/security/Kconfig b/security/Kconfig
index d23c839..c0538e6 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 DEFAULT_LSM_MMAP_MIN_ADDR
+ int "Low address space for LSM to from user allocation"
+ depends on SECURITY
+ default 32768
+ 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/selinux/hooks.c b/security/selinux/hooks.c
index e65677d..9182c27 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3034,7 +3034,7 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
int rc = 0;
u32 sid = current_sid();

- if (addr < mmap_min_addr)
+ if (addr < CONFIG_DEFAULT_LSM_MMAP_MIN_ADDR)
rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
MEMPROTECT__MMAP_ZERO, NULL);
if (rc || addr_only)


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