Security: Introduce security= boot parameter

Add the security= boot parameter. This is done to avoid LSM
registration clashes in case of more than one bult-in module.

User can choose a security module to enable at boot. If no
security= boot parameter is specified, only the first LSM
asking for registration will be loaded. An invalid security
module name will be treated as if no module has been chosen.

LSM modules must check now if they are allowed to register
by calling security_module_enable(ops) first. Modify SELinux
and SMACK to do so.

Do not let SMACK register smackfs if it was not chosen on
boot. Smackfs assumes that smack hooks are registered and
the initial task security setup (swapper->security) is done.

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Acked-by: James Morris <jmorris@namei.org>

3 files changed, 18 insertions, 2 deletions

diff --git a/security/smack/smack.h b/security/smack/smack.h
index 62c1e982849d..4a4477f5afdc 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -15,6 +15,7 @@
 
 #include <linux/capability.h>
 #include <linux/spinlock.h>
+#include <linux/security.h>
 #include <net/netlabel.h>
 
 /*
@@ -187,6 +188,7 @@ extern struct smack_known smack_known_star;
 extern struct smack_known smack_known_unset;
 
 extern struct smk_list_entry *smack_list;
+extern struct security_operations smack_ops;
 
 /*
  * Stricly for CIPSO level manipulation.
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 732ba27923c4..904bdc01a12b 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2424,7 +2424,9 @@ static void smack_release_secctx(char *secdata, u32 seclen)
 {
 }
 
-static struct security_operations smack_ops = {
+struct security_operations smack_ops = {
+	.name =				"smack",
+
 	.ptrace = 			smack_ptrace,
 	.capget = 			cap_capget,
 	.capset_check = 		cap_capset_check,
@@ -2557,6 +2559,9 @@ static struct security_operations smack_ops = {
  */
 static __init int smack_init(void)
 {
+	if (!security_module_enable(&smack_ops))
+		return 0;
+
 	printk(KERN_INFO "Smack:  Initializing.\n");
 
 	/*
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index cfae8afcc262..6ba283783b70 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -965,12 +965,21 @@ static struct vfsmount *smackfs_mount;
  *
  * register the smackfs
  *
- * Returns 0 unless the registration fails.
+ * Do not register smackfs if Smack wasn't enabled
+ * on boot. We can not put this method normally under the
+ * smack_init() code path since the security subsystem get
+ * initialized before the vfs caches.
+ *
+ * Returns true if we were not chosen on boot or if
+ * we were chosen and filesystem registration succeeded.
  */
 static int __init init_smk_fs(void)
 {
 	int err;
 
+	if (!security_module_enable(&smack_ops))
+		return 0;
+
 	err = register_filesystem(&smk_fs_type);
 	if (!err) {
 		smackfs_mount = kern_mount(&smk_fs_type);