TOMOYO: Use RCU primitives for list operation

Replace list operation with RCU primitives and replace
down_read()/up_read() with srcu_read_lock()/srcu_read_unlock().
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/tomoyo/common.h

@@ -269,6 +269,8 @@ struct tomoyo_io_buffer {
 	int (*write) (struct tomoyo_io_buffer *);
 	/* Exclusive lock for this structure.   */
 	struct mutex io_sem;
+	/* Index returned by tomoyo_read_lock(). */
+	int reader_idx;
 	/* The position currently reading from. */
 	struct list_head *read_var1;
 	/* Extra variables for reading.         */
@@ -446,16 +448,28 @@ extern struct tomoyo_domain_info tomoyo_kernel_domain;
  * @cookie:     the &struct list_head to use as a cookie.
  * @head:       the head for your list.
  *
- * Same with list_for_each() except that this primitive uses @cookie
+ * Same with list_for_each_rcu() except that this primitive uses @cookie
  * so that we can continue iteration.
  * @cookie must be NULL when iteration starts, and @cookie will become
  * NULL when iteration finishes.
  */
-#define list_for_each_cookie(pos, cookie, head)                       \
-	for (({ if (!cookie)                                          \
-				     cookie = head; }),               \
-	     pos = (cookie)->next;                                    \
-	     prefetch(pos->next), pos != (head) || ((cookie) = NULL); \
-	     (cookie) = pos, pos = pos->next)
+#define list_for_each_cookie(pos, cookie, head)				\
+	for (({ if (!cookie)						\
+				     cookie = head; }),			\
+		     pos = rcu_dereference((cookie)->next);		\
+	     prefetch(pos->next), pos != (head) || ((cookie) = NULL);	\
+	     (cookie) = pos, pos = rcu_dereference(pos->next))
+
+extern struct srcu_struct tomoyo_ss;
+
+static inline int tomoyo_read_lock(void)
+{
+	return srcu_read_lock(&tomoyo_ss);
+}
+
+static inline void tomoyo_read_unlock(int idx)
+{
+	srcu_read_unlock(&tomoyo_ss, idx);
+}
 
 #endif /* !defined(_SECURITY_TOMOYO_COMMON_H) */

security/tomoyo/realpath.c

@@ -402,11 +402,13 @@ void __init tomoyo_realpath_init(void)
 		INIT_LIST_HEAD(&tomoyo_name_list[i]);
 	INIT_LIST_HEAD(&tomoyo_kernel_domain.acl_info_list);
 	tomoyo_kernel_domain.domainname = tomoyo_save_name(TOMOYO_ROOT_NAME);
-	list_add_tail(&tomoyo_kernel_domain.list, &tomoyo_domain_list);
-	down_read(&tomoyo_domain_list_lock);
+	/*
+	 * tomoyo_read_lock() is not needed because this function is
+	 * called before the first "delete" request.
+	 */
+	list_add_tail_rcu(&tomoyo_kernel_domain.list, &tomoyo_domain_list);
 	if (tomoyo_find_domain(TOMOYO_ROOT_NAME) != &tomoyo_kernel_domain)
 		panic("Can't register tomoyo_kernel_domain");
-	up_read(&tomoyo_domain_list_lock);
 }
 
 /* Memory allocated for temporary purpose. */

security/tomoyo/tomoyo.c

@@ -76,8 +76,18 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
 	 * Execute permission is checked against pathname passed to do_execve()
 	 * using current domain.
 	 */
-	if (!domain)
-		return tomoyo_find_next_domain(bprm);
+	if (!domain) {
+		/*
+		 * We will need to protect whole execve() operation when GC
+		 * starts kfree()ing "struct tomoyo_domain_info" because
+		 * bprm->cred->security points to "struct tomoyo_domain_info"
+		 * but "struct tomoyo_domain_info" does not have a refcounter.
+		 */
+		const int idx = tomoyo_read_lock();
+		const int err = tomoyo_find_next_domain(bprm);
+		tomoyo_read_unlock(idx);
+		return err;
+	}
 	/*
 	 * Read permission is checked against interpreters using next domain.
 	 * '1' is the result of open_to_namei_flags(O_RDONLY).
@@ -278,6 +288,9 @@ static struct security_operations tomoyo_security_ops = {
 	.sb_pivotroot        = tomoyo_sb_pivotroot,
 };
 
+/* Lock for GC. */
+struct srcu_struct tomoyo_ss;
+
 static int __init tomoyo_init(void)
 {
 	struct cred *cred = (struct cred *) current_cred();
@@ -285,7 +298,8 @@ static int __init tomoyo_init(void)
 	if (!security_module_enable(&tomoyo_security_ops))
 		return 0;
 	/* register ourselves with the security framework */
-	if (register_security(&tomoyo_security_ops))
+	if (register_security(&tomoyo_security_ops) ||
+	    init_srcu_struct(&tomoyo_ss))
 		panic("Failure registering TOMOYO Linux");
 	printk(KERN_INFO "TOMOYO Linux initialized\n");
 	cred->security = &tomoyo_kernel_domain;