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SubjectRe: [PATCH] Protection for exploiting null dereference using mmap
From
Date
On Tue, 2007-06-05 at 17:16 -0400, Alan Cox wrote:
> On Tue, Jun 05, 2007 at 05:00:51PM -0400, James Morris wrote:
> > This should be an unsigned long.
> >
> > I wonder if the default should be for this value to be zero (i.e. preserve
> > existing behavior). It could break binaries, albeit potentially insecure
>
> Agreed - DOSemu type apps and lrmi need to map at zero for vm86

And so it shall be!

Signed-off-by: Eric Paris <eparis@redhat.com>

---
Documentation/sysctl/kernel.txt | 14 ++++++++++++++
include/linux/security.h | 17 ++++++++++++-----
kernel/sysctl.c | 8 ++++++++
mm/mmap.c | 4 ++--
mm/mremap.c | 13 +++++++++++--
mm/nommu.c | 2 +-
security/dummy.c | 6 +++++-
security/security.c | 2 ++
security/selinux/hooks.c | 12 ++++++++----
security/selinux/include/av_perm_to_string.h | 1 +
security/selinux/include/av_permissions.h | 1 +
security/selinux/include/class_to_string.h | 1 +
security/selinux/include/flask.h | 1 +
13 files changed, 67 insertions(+), 15 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 111fd28..be3991c 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -29,6 +29,7 @@ show up in /proc/sys/kernel:
- java-interpreter [ binfmt_java, obsolete ]
- kstack_depth_to_print [ X86 only ]
- l2cr [ PPC only ]
+- mmap_min_addr
- modprobe ==> Documentation/kmod.txt
- msgmax
- msgmnb
@@ -178,6 +179,19 @@ kernel stack.

==============================================================

+mmap_min_addr
+
+This file indicates the amount of address space which a user process will be
+restricted from mmaping. Since kernel null dereference bugs could
+accidentally operate based on the information in the first couple of pages of
+memory userspace processes should not be allowed to write to them. By default
+this value is set to 0 and no protections will be enforced by the security
+module. Setting this value to something like 64k will allow the vast majority
+of applications to work correctly and provide defense in depth against future
+potential kernel bugs.
+
+==============================================================
+
osrelease, ostype & version:

# cat osrelease
diff --git a/include/linux/security.h b/include/linux/security.h
index 9eb9e0f..c11dc8a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -71,6 +71,7 @@ struct xfrm_user_sec_ctx;
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
*/
@@ -1241,8 +1242,9 @@ struct security_operations {
int (*file_ioctl) (struct file * file, unsigned int cmd,
unsigned long arg);
int (*file_mmap) (struct file * file,
- unsigned long reqprot,
- unsigned long prot, unsigned long flags);
+ unsigned long reqprot, unsigned long prot,
+ unsigned long flags, unsigned long addr,
+ unsigned long addr_only);
int (*file_mprotect) (struct vm_area_struct * vma,
unsigned long reqprot,
unsigned long prot);
@@ -1814,9 +1816,12 @@ static inline int security_file_ioctl (struct file *file, unsigned int cmd,

static inline int security_file_mmap (struct file *file, unsigned long reqprot,
unsigned long prot,
- unsigned long flags)
+ unsigned long flags,
+ unsigned long addr,
+ unsigned long addr_only)
{
- return security_ops->file_mmap (file, reqprot, prot, flags);
+ return security_ops->file_mmap (file, reqprot, prot, flags, addr,
+ addr_only);
}

static inline int security_file_mprotect (struct vm_area_struct *vma,
@@ -2489,7 +2494,9 @@ static inline int security_file_ioctl (struct file *file, unsigned int cmd,

static inline int security_file_mmap (struct file *file, unsigned long reqprot,
unsigned long prot,
- unsigned long flags)
+ unsigned long flags,
+ unsigned long addr,
+ unsigned long addr_only)
{
return 0;
}
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 30ee462..a6feef2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -615,6 +615,14 @@ static ctl_table kern_table[] = {
.proc_handler = &proc_dointvec,
},
#endif
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "mmap_min_addr",
+ .data = &mmap_min_addr,
+ .maxlen = sizeof(unsigned long),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },

{ .ctl_name = 0 }
};
diff --git a/mm/mmap.c b/mm/mmap.c
index 68b9ad2..bce4995 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1023,10 +1023,10 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
}
}

- error = security_file_mmap(file, reqprot, prot, flags);
+ error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
if (error)
return error;
-
+
/* Clear old maps */
error = -ENOMEM;
munmap_back:
diff --git a/mm/mremap.c b/mm/mremap.c
index 5d4bd4f..bc7c52e 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -291,6 +291,10 @@ unsigned long do_mremap(unsigned long addr,
if ((addr <= new_addr) && (addr+old_len) > new_addr)
goto out;

+ ret = security_file_mmap(0, 0, 0, 0, new_addr, 1);
+ if (ret)
+ goto out;
+
ret = do_munmap(mm, new_addr, new_len);
if (ret)
goto out;
@@ -390,8 +394,13 @@ unsigned long do_mremap(unsigned long addr,

new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
vma->vm_pgoff, map_flags);
- ret = new_addr;
- if (new_addr & ~PAGE_MASK)
+ if (new_addr & ~PAGE_MASK) {
+ ret = new_addr;
+ goto out;
+ }
+
+ ret = security_file_mmap(0, 0, 0, 0, new_addr, 1);
+ if (ret)
goto out;
}
ret = move_vma(vma, addr, old_len, new_len, new_addr);
diff --git a/mm/nommu.c b/mm/nommu.c
index 2b16b00..6f8ddee 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -639,7 +639,7 @@ static int validate_mmap_request(struct file *file,
}

/* allow the security API to have its say */
- ret = security_file_mmap(file, reqprot, prot, flags);
+ ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
if (ret < 0)
return ret;

diff --git a/security/dummy.c b/security/dummy.c
index 8ffd764..d6a112c 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -420,8 +420,12 @@ static int dummy_file_ioctl (struct file *file, unsigned int command,

static int dummy_file_mmap (struct file *file, unsigned long reqprot,
unsigned long prot,
- unsigned long flags)
+ unsigned long flags,
+ unsigned long addr,
+ unsigned long addr_only)
{
+ if (addr < mmap_min_addr)
+ return -EACCES;
return 0;
}

diff --git a/security/security.c b/security/security.c
index fc8601b..024484f 100644
--- a/security/security.c
+++ b/security/security.c
@@ -24,6 +24,7 @@ extern struct security_operations dummy_security_ops;
extern void security_fixup_ops(struct security_operations *ops);

struct security_operations *security_ops; /* Initialized to NULL */
+unsigned long mmap_min_addr; /* 0 means no protection */

static inline int verify(struct security_operations *ops)
{
@@ -176,4 +177,5 @@ EXPORT_SYMBOL_GPL(register_security);
EXPORT_SYMBOL_GPL(unregister_security);
EXPORT_SYMBOL_GPL(mod_reg_security);
EXPORT_SYMBOL_GPL(mod_unreg_security);
+EXPORT_SYMBOL_GPL(mmap_min_addr);
EXPORT_SYMBOL(security_ops);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ad8dd4e..2b44832 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2568,12 +2568,16 @@ static int file_map_prot_check(struct file *file, unsigned long prot, int shared
}

static int selinux_file_mmap(struct file *file, unsigned long reqprot,
- unsigned long prot, unsigned long flags)
+ unsigned long prot, unsigned long flags,
+ unsigned long addr, unsigned long addr_only)
{
- int rc;
+ int rc = 0;
+ u32 sid = ((struct task_security_struct*)(current->security))->sid;

- rc = secondary_ops->file_mmap(file, reqprot, prot, flags);
- if (rc)
+ if (addr < mmap_min_addr)
+ rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
+ MEMPROTECT__MMAP_ZERO, NULL);
+ if (rc || addr_only)
return rc;

if (selinux_checkreqprot)
diff --git a/security/selinux/include/av_perm_to_string.h b/security/selinux/include/av_perm_to_string.h
index b83e740..049bf69 100644
--- a/security/selinux/include/av_perm_to_string.h
+++ b/security/selinux/include/av_perm_to_string.h
@@ -158,3 +158,4 @@
S_(SECCLASS_KEY, KEY__CREATE, "create")
S_(SECCLASS_DCCP_SOCKET, DCCP_SOCKET__NODE_BIND, "node_bind")
S_(SECCLASS_DCCP_SOCKET, DCCP_SOCKET__NAME_CONNECT, "name_connect")
+ S_(SECCLASS_MEMPROTECT, MEMPROTECT__MMAP_ZERO, "mmap_zero")
diff --git a/security/selinux/include/av_permissions.h b/security/selinux/include/av_permissions.h
index 5fee173..eda89a2 100644
--- a/security/selinux/include/av_permissions.h
+++ b/security/selinux/include/av_permissions.h
@@ -823,3 +823,4 @@
#define DCCP_SOCKET__NAME_BIND 0x00200000UL
#define DCCP_SOCKET__NODE_BIND 0x00400000UL
#define DCCP_SOCKET__NAME_CONNECT 0x00800000UL
+#define MEMPROTECT__MMAP_ZERO 0x00000001UL
diff --git a/security/selinux/include/class_to_string.h b/security/selinux/include/class_to_string.h
index 3787990..e77de0e 100644
--- a/security/selinux/include/class_to_string.h
+++ b/security/selinux/include/class_to_string.h
@@ -63,3 +63,4 @@
S_("key")
S_(NULL)
S_("dccp_socket")
+ S_("memprotect")
diff --git a/security/selinux/include/flask.h b/security/selinux/include/flask.h
index 35f309f..a9c2b20 100644
--- a/security/selinux/include/flask.h
+++ b/security/selinux/include/flask.h
@@ -49,6 +49,7 @@
#define SECCLASS_PACKET 57
#define SECCLASS_KEY 58
#define SECCLASS_DCCP_SOCKET 60
+#define SECCLASS_MEMPROTECT 61

/*
* Security identifier indices for initial entities

-
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