Message-ID: <20080305152901.GA26016@ubuntu>
Date:	Wed, 5 Mar 2008 17:29:01 +0200
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Chris Wright <chrisw@...s-sol.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Paul Moore <paul.moore@...com>,
	Alexey Dobriyan <adobriyan@...ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus <torvalds@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	LSM-ML <linux-security-module@...r.kernel.org>
Subject: [PATCH -v7 -rc3] Security: Introduce security= boot parameter

Hi!,

[
    Our usual changelog:

    - Fold the SMACK bugfix here cause now it depends on the
      new introduced security_ symbol.
    - Do not register smackfs if Smack was not loaded
    - Do not use a global to check if Smack was enabled, use 
      security_module_enable(ops) instead.
    - Export smack_ops security operations to the rest of
      SMACK code to satisfy above point.
    - Remove James ACK cause patch semantics changed (could you
      please reACK ?).
]

-->

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@...il.com>
Reported-by: Alexey Dobriyan <adobriyan@...ru>
---

 Documentation/kernel-parameters.txt |    6 ++++
 include/linux/security.h            |   12 +++++++++
 security/dummy.c                    |    2 -
 security/security.c                 |   46 +++++++++++++++++++++++++++++++++++-
 security/selinux/hooks.c            |    7 +++++
 security/smack/smack.h              |    2 +
 security/smack/smack_lsm.c          |    7 ++++-
 security/smack/smackfs.c            |    9 ++++++-

 8 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9a5b665..64efbdc 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -374,6 +374,12 @@ and is between 256 and 4096 characters. It is defined in the file
 			possible to determine what the correct size should be.
 			This option provides an override for these situations.
 
+	security=	[SECURITY] Choose a security module to enable at boot. 
+			If this boot parameter is not specified, only the first 
+			security module asking for security registration will be
+			loaded. An invalid security module name will be treated
+			as if no module has been chosen.
+
 	capability.disable=
 			[SECURITY] Disable capabilities.  This would normally
 			be used only if an alternative security model is to be
diff --git a/include/linux/security.h b/include/linux/security.h
index fe52cde..801c9ad 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -42,6 +42,9 @@
 
 extern unsigned securebits;
 
+/* Maximum number of letters for an LSM name string */
+#define SECURITY_NAME_MAX	10
+
 struct ctl_table;
 
 /*
@@ -117,6 +120,12 @@ struct request_sock;
 /**
  * struct security_operations - main security structure
  *
+ * Security module identifier.
+ *
+ * @name:
+ *	A string that acts as a unique identifeir for the LSM with max number
+ *	of characters = SECURITY_NAME_MAX.
+ *
  * Security hooks for program execution operations.
  *
  * @bprm_alloc_security:
@@ -1207,6 +1216,8 @@ struct request_sock;
  * This is the main security structure.
  */
 struct security_operations {
+	char name[SECURITY_NAME_MAX + 1];
+
 	int (*ptrace) (struct task_struct * parent, struct task_struct * child);
 	int (*capget) (struct task_struct * target,
 		       kernel_cap_t * effective,
@@ -1466,6 +1477,7 @@ struct security_operations {
 
 /* prototypes */
 extern int security_init	(void);
+extern int security_module_enable(struct security_operations *ops);
 extern int register_security	(struct security_operations *ops);
 extern int mod_reg_security	(const char *name, struct security_operations *ops);
 extern struct dentry *securityfs_create_file(const char *name, mode_t mode,
diff --git a/security/dummy.c b/security/dummy.c
index 649326b..96d196f 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -979,7 +979,7 @@ static inline int dummy_key_permission(key_ref_t key_ref,
 }
 #endif /* CONFIG_KEYS */
 
-struct security_operations dummy_security_ops;
+struct security_operations dummy_security_ops = { "dummy" };
 
 #define set_to_dummy_if_null(ops, function)				\
 	do {								\
diff --git a/security/security.c b/security/security.c
index d15e56c..f188672 100644
--- a/security/security.c
+++ b/security/security.c
@@ -17,6 +17,9 @@
 #include <linux/kernel.h>
 #include <linux/security.h>
 
+/* Boot-time LSM user choice */
+static spinlock_t chosen_lsm_lock;
+static char chosen_lsm[SECURITY_NAME_MAX + 1];
 
 /* things that live in dummy.c */
 extern struct security_operations dummy_security_ops;
@@ -62,18 +65,59 @@ int __init security_init(void)
 	}
 
 	security_ops = &dummy_security_ops;
+	spin_lock_init(&chosen_lsm_lock);
 	do_security_initcalls();
 
 	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.
+ *
+ * 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.
+ * Otherwise, return false.
+ */
+int security_module_enable(struct security_operations *ops)
+{
+	int rc = 1;
+
+	spin_lock(&chosen_lsm_lock);
+	if (!*chosen_lsm)
+		strncpy(chosen_lsm, ops->name, SECURITY_NAME_MAX);
+	else if (strncmp(ops->name, chosen_lsm, SECURITY_NAME_MAX))
+		rc = 0;
+	spin_unlock(&chosen_lsm_lock);
+
+	if (rc)
+		printk(KERN_INFO "Security: Loading '%s' security module.\n",
+		       ops->name);
+
+	return rc;
+}
+
 /**
  * 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 75c2e99..49709a4 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5219,6 +5219,8 @@ 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,
@@ -5405,6 +5407,11 @@ 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 a21a0e9..c444f48 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>
 
 /*
@@ -195,6 +196,7 @@ 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 770eb06..afa7967 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2433,7 +2433,9 @@ 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,
@@ -2566,6 +2568,9 @@ 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 358c92c..769da9a 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -986,12 +986,19 @@ 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.
+ *
+ * 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);

-- 

"Better to light a candle, than curse the darkness"

Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com

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