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Date: Wed, 06 Jun 2007 13:30:40 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Eric Paris <eparis@...hat.com>
Cc: Alan Cox <alan@...hat.com>, James Morris <jmorris@...ei.org>,
linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
drepper@...hat.com, roland@...hat.com, arjan@...radead.org,
mingo@...e.hu, viro@...iv.linux.org.uk, chrisw@...hat.com,
sgrubb@...hat.com
Subject: Re: [PATCH] Protection for exploiting null dereference using mmap
On Wed, 2007-06-06 at 02:30 -0400, Eric Paris wrote:
> 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@...hat.com>
With the fix already noted by James,
Acked-by: Stephen Smalley <sds@...ho.nsa.gov>
Note that you need to also submit a patch for policy to reserve that
class to avoid future collisions.
>
> ---
>
> 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
>
>
>
> --
> This message was distributed to subscribers of the selinux mailing list.
> If you no longer wish to subscribe, send mail to majordomo@...ho.nsa.gov with
> the words "unsubscribe selinux" without quotes as the message.
--
Stephen Smalley
National Security Agency
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