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>

6 files changed, 65 insertions, 4 deletions

diff --git a/security/dummy.c b/security/dummy.c
index 1ac9f8e..d797a41 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -1017,7 +1017,9 @@ static inline void dummy_audit_rule_free(void *lsmrule)
 
 #endif /* CONFIG_AUDIT */
 
-struct security_operations dummy_security_ops;
+struct security_operations dummy_security_ops = {
+	.name = "dummy",
+};
 
 #define set_to_dummy_if_null(ops, function)				\
 	do {								\
diff --git a/security/security.c b/security/security.c
index 2ef593e..dd0c6ba 100644
--- a/security/security.c
+++ b/security/security.c
@@ -17,6 +17,8 @@
 #include <linux/kernel.h>
 #include <linux/security.h>
 
+/* Boot-time LSM user choice */
+static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1];
 
 /* things that live in dummy.c */
 extern struct security_operations dummy_security_ops;
@@ -67,13 +69,47 @@ int __init security_init(void)
 	return 0;
 }
 
+/* Save user chosen LSM */
+static int __init choose_lsm(char *str)
+{
+	strncpy(chosen_lsm, str, SECURITY_NAME_MAX);
+	return 1;
+}
+__setup("security=", choose_lsm);
+
+/**
+ * security_module_enable - Load given security module on boot ?
+ * @ops: a pointer to the struct security_operations that is to be checked.
+ *
+ * Each LSM must pass this method before registering its own operations
+ * to avoid security registration races. This method may also be used
+ * to check if your LSM is currently loaded.
+ *
+ * Return true if:
+ *	-The passed LSM is the one chosen by user at boot time,
+ *	-or user didsn't specify a specific LSM and we're the first to ask
+ *	 for registeration permissoin,
+ *	-or the passed LSM is currently loaded.
+ * Otherwise, return false.
+ */
+int __init security_module_enable(struct security_operations *ops)
+{
+	if (!*chosen_lsm)
+		strncpy(chosen_lsm, ops->name, SECURITY_NAME_MAX);
+	else if (strncmp(ops->name, chosen_lsm, SECURITY_NAME_MAX))
+		return 0;
+
+	return 1;
+}
+
 /**
  * register_security - registers a security framework with the kernel
  * @ops: a pointer to the struct security_options that is to be registered
  *
  * This function is to allow a security module to register itself with the
  * kernel security subsystem.  Some rudimentary checking is done on the @ops
- * value passed to this function.
+ * value passed to this function. You'll need to check first if your LSM
+ * is allowed to register its @ops by calling security_module_enable(@ops).
  *
  * If there is already a security module registered with the kernel,
  * an error will be returned.  Otherwise 0 is returned on success.
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a2f7e9c..f9927f0 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5295,6 +5295,8 @@ static int selinux_key_permission(key_ref_t key_ref,
 #endif
 
 static struct security_operations selinux_ops = {
+	.name =				"selinux",
+
 	.ptrace =			selinux_ptrace,
 	.capget =			selinux_capget,
 	.capset_check =			selinux_capset_check,
@@ -5492,6 +5494,11 @@ static __init int selinux_init(void)
 {
 	struct task_security_struct *tsec;
 
+	if (!security_module_enable(&selinux_ops)) {
+		selinux_enabled = 0;
+		return 0;
+	}
+
 	if (!selinux_enabled) {
 		printk(KERN_INFO "SELinux:  Disabled at boot.\n");
 		return 0;
diff --git a/security/smack/smack.h b/security/smack/smack.h
index 62c1e98..4a4477f 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 732ba27..904bdc0 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 cfae8af..6ba2837 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);