Commit f22f9aaf authored by Paul Moore's avatar Paul Moore
Browse files

selinux: remove the runtime disable functionality 



After working with the larger SELinux-based distros for several
years, we're finally at a place where we can disable the SELinux
runtime disable functionality.  The existing kernel deprecation
notice explains the functionality and why we want to remove it:

  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.

It is that last sentence, mentioning the '__ro_after_init' hardening,
which is the real motivation for this change, and if you look at the
diffstat you'll see that the impact of this patch reaches across all
the different LSMs, helping prevent tampering at the LSM hook level.

From a SELinux perspective, it is important to note that if you
continue to disable SELinux via "/etc/selinux/config" it may appear
that SELinux is disabled, but it is simply in an uninitialized state.
If you load a policy with `load_policy -i`, you will see SELinux
come alive just as if you had loaded the policy during early-boot.

It is also worth noting that the "/sys/fs/selinux/disable" file is
always writable now, regardless of the Kconfig settings, but writing
to the file has no effect on the system, other than to display an
error on the console if a non-zero/true value is written.

Finally, in the several years where we have been working on
deprecating this functionality, there has only been one instance of
someone mentioning any user visible breakage.  In this particular
case it was an individual's kernel test system, and the workaround
documented in the deprecation notice ("selinux=0" on the kernel
command line) resolved the issue without problem.

Acked-by: default avatarCasey Schaufler <casey@schaufler-ca.com>
Signed-off-by: default avatarPaul Moore <paul@paul-moore.com>
parent a7e4676e

Documentation/ABI/obsolete/sysfs-selinux-disable→Documentation/ABI/removed/sysfs-selinux-disable

+3 −0
Original line number Diff line number Diff line
@@ -4,6 +4,9 @@ KernelVersion: 2.6.12-rc2 (predates git) 
Contact:	selinux@vger.kernel.org

Description:



	REMOVAL UPDATE: The SELinux runtime disable functionality was removed

	in March 2023, the original deprecation notice is shown below.



	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.

include/linux/lsm_hooks.h

+0 −7
Original line number Diff line number Diff line
@@ -1763,13 +1763,6 @@ static inline void security_delete_hooks(struct security_hook_list *hooks, 
}

#endif /* CONFIG_SECURITY_SELINUX_DISABLE */



/* Currently required to handle SELinux runtime hook disable. */

#ifdef CONFIG_SECURITY_WRITABLE_HOOKS

#define __lsm_ro_after_init

#else

#define __lsm_ro_after_init	__ro_after_init

#endif /* CONFIG_SECURITY_WRITABLE_HOOKS */



extern int lsm_inode_alloc(struct inode *inode);



#endif /* ! __LINUX_LSM_HOOKS_H */

security/Kconfig

+0 −5
Original line number Diff line number Diff line
@@ -32,11 +32,6 @@ config SECURITY 


	  If you are unsure how to answer this question, answer N.



config SECURITY_WRITABLE_HOOKS

	depends on SECURITY

	bool

	default n



config SECURITYFS

	bool "Enable the securityfs filesystem"

	help

security/apparmor/lsm.c

+3 −3
Original line number Diff line number Diff line
@@ -1209,13 +1209,13 @@ static int apparmor_inet_conn_request(const struct sock *sk, struct sk_buff *skb 
/*

 * The cred blob is a pointer to, not an instance of, an aa_label.

 */

struct lsm_blob_sizes apparmor_blob_sizes __lsm_ro_after_init = {

struct lsm_blob_sizes apparmor_blob_sizes __ro_after_init = {

	.lbs_cred = sizeof(struct aa_label *),

	.lbs_file = sizeof(struct aa_file_ctx),

	.lbs_task = sizeof(struct aa_task_ctx),

};



static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {

static struct security_hook_list apparmor_hooks[] __ro_after_init = {

	LSM_HOOK_INIT(ptrace_access_check, apparmor_ptrace_access_check),

	LSM_HOOK_INIT(ptrace_traceme, apparmor_ptrace_traceme),

	LSM_HOOK_INIT(capget, apparmor_capget),
@@ -1427,7 +1427,7 @@ static const struct kernel_param_ops param_ops_aaintbool = { 
	.get = param_get_aaintbool

};

/* Boot time disable flag */

static int apparmor_enabled __lsm_ro_after_init = 1;

static int apparmor_enabled __ro_after_init = 1;

module_param_named(enabled, apparmor_enabled, aaintbool, 0444);



static int __init apparmor_enabled_setup(char *str)

security/bpf/hooks.c

+2 −2
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 
#include <linux/lsm_hooks.h>

#include <linux/bpf_lsm.h>



static struct security_hook_list bpf_lsm_hooks[] __lsm_ro_after_init = {

static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {

	#define LSM_HOOK(RET, DEFAULT, NAME, ...) \

	LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),

	#include <linux/lsm_hook_defs.h>
@@ -22,7 +22,7 @@ static int __init bpf_lsm_init(void) 
	return 0;

}



struct lsm_blob_sizes bpf_lsm_blob_sizes __lsm_ro_after_init = {

struct lsm_blob_sizes bpf_lsm_blob_sizes __ro_after_init = {

	.lbs_inode = sizeof(struct bpf_storage_blob),

	.lbs_task = sizeof(struct bpf_storage_blob),

};