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selinux: deprecate disabling SELinux and runtime

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Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
code was originally developed to make it easier for Linux
distributions to support architectures where adding parameters to the
kernel command line was difficult.  Unfortunately, supporting runtime
disable meant we had to make some security trade-offs when it came to
the LSM hooks, as documented in the Kconfig help text:

  NOTE: selecting this option will disable the '__ro_after_init'
  kernel hardening feature for security hooks.   Please consider
  using the selinux=0 boot parameter instead of enabling this
  option.

Fortunately it looks as if that the original motivation for the
runtime disable functionality is gone, and Fedora/RHEL appears to be
the only major distribution enabling this capability at build time
so we are now taking steps to remove it entirely from the kernel.
The first step is to mark the functionality as deprecated and print
an error when it is used (what this patch is doing).  As Fedora/RHEL
makes progress in transitioning the distribution away from runtime
disable, we will introduce follow-up patches over several kernel
releases which will block for increasing periods of time when the
runtime disable is used.  Finally we will remove the option entirely
once we believe all users have moved to the kernel cmdline approach.

Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Paul Moore 2019-12-18 21:45:08 -05:00
parent 7a4b519474
commit 89b223bfb8
4 changed files with 37 additions and 0 deletions
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26
Documentation/ABI/obsolete/sysfs-selinux-disable Normal file
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@ -0,0 +1,26 @@
What: /sys/fs/selinux/disable
Date: April 2005 (predates git)
KernelVersion: 2.6.12-rc2 (predates git)
Contact: selinux@vger.kernel.org
Description:
The selinuxfs "disable" node allows SELinux to be disabled at runtime
prior to a policy being loaded into the kernel. If disabled via this
mechanism, SELinux will remain disabled until the system is rebooted.
The preferred method of disabling SELinux is via the "selinux=0" boot
parameter, but the selinuxfs "disable" node was created to make it
easier for systems with primitive bootloaders that did not allow for
easy modification of the kernel command line. Unfortunately, allowing
for SELinux to be disabled at runtime makes it difficult to secure the
kernel's LSM hooks using the "__ro_after_init" feature.
Thankfully, the need for the SELinux runtime disable appears to be
gone, the default Kconfig configuration disables this selinuxfs node,
and only one of the major distributions, Fedora, supports disabling
SELinux at runtime. Fedora is in the process of removing the
selinuxfs "disable" node and once that is complete we will start the
slow process of removing this code from the kernel.
More information on /sys/fs/selinux/disable can be found under the
CONFIG_SECURITY_SELINUX_DISABLE Kconfig option.

1
MAINTAINERS
View File

@ -14806,6 +14806,7 @@ F: include/uapi/linux/selinux_netlink.h
F: security/selinux/
F: scripts/selinux/
F: Documentation/admin-guide/LSM/SELinux.rst
F: Documentation/ABI/obsolete/sysfs-selinux-disable
SENSABLE PHANTOM
M: Jiri Slaby <jirislaby@gmail.com>

3
security/selinux/Kconfig
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@ -42,6 +42,9 @@ config SECURITY_SELINUX_DISABLE
using the selinux=0 boot parameter instead of enabling this
option.
WARNING: this option is deprecated and will be removed in a future
kernel release.
If you are unsure how to answer this question, answer N.
config SECURITY_SELINUX_DEVELOP

7
security/selinux/selinuxfs.c
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@ -281,6 +281,13 @@ static ssize_t sel_write_disable(struct file *file, const char __user *buf,
int new_value;
int enforcing;
/* NOTE: we are now officially considering runtime disable as
* deprecated, and using it will become increasingly painful
* (e.g. sleeping/blocking) as we progress through future
* kernel releases until eventually it is removed
*/
pr_err("SELinux: Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
if (count >= PAGE_SIZE)
return -ENOMEM;