TOMOYO: Fix lockdep warning.

Currently TOMOYO holds SRCU lock upon open() and releases it upon close()
because list elements stored in the "struct tomoyo_io_buffer" instances are
accessed until close() is called. However, such SRCU usage causes lockdep to
complain about leaving the kernel with SRCU lock held.

This patch solves the warning by holding/releasing SRCU upon each
read()/write(). This patch is doing something similar to calling kfree()
without calling synchronize_srcu(), by selectively deferring kfree() by keeping
track of the "struct tomoyo_io_buffer" instances.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

security/tomoyo/common.c

@@ -1820,9 +1820,7 @@ static void tomoyo_read_self_domain(struct tomoyo_io_buffer *head)
  * @type: Type of interface.
  * @file: Pointer to "struct file".
  *
- * Associates policy handler and returns 0 on success, -ENOMEM otherwise.
- *
- * Caller acquires tomoyo_read_lock().
+ * Returns 0 on success, negative value otherwise.
  */
 int tomoyo_open_control(const u8 type, struct file *file)
 {
@@ -1921,9 +1919,6 @@ int tomoyo_open_control(const u8 type, struct file *file)
 			return -ENOMEM;
 		}
 	}
-	if (type != TOMOYO_QUERY && type != TOMOYO_AUDIT)
-		head->reader_idx = tomoyo_read_lock();
-	file->private_data = head;
 	/*
 	 * If the file is /sys/kernel/security/tomoyo/query , increment the
 	 * observer counter.
@@ -1932,6 +1927,8 @@ int tomoyo_open_control(const u8 type, struct file *file)
 	 */
 	if (type == TOMOYO_QUERY)
 		atomic_inc(&tomoyo_query_observers);
+	file->private_data = head;
+	tomoyo_notify_gc(head, true);
 	return 0;
 }
 
@@ -2000,13 +1997,12 @@ static inline bool tomoyo_has_more_namespace(struct tomoyo_io_buffer *head)
  * @buffer_len: Size of @buffer.
  *
  * Returns bytes read on success, negative value otherwise.
- *
- * Caller holds tomoyo_read_lock().
  */
 int tomoyo_read_control(struct tomoyo_io_buffer *head, char __user *buffer,
 			const int buffer_len)
 {
 	int len;
+	int idx;
 
 	if (!head->read)
 		return -ENOSYS;
@@ -2014,6 +2010,7 @@ int tomoyo_read_control(struct tomoyo_io_buffer *head, char __user *buffer,
 		return -EINTR;
 	head->read_user_buf = buffer;
 	head->read_user_buf_avail = buffer_len;
+	idx = tomoyo_read_lock();
 	if (tomoyo_flush(head))
 		/* Call the policy handler. */
 		do {
@@ -2021,6 +2018,7 @@ int tomoyo_read_control(struct tomoyo_io_buffer *head, char __user *buffer,
 			head->read(head);
 		} while (tomoyo_flush(head) &&
 			 tomoyo_has_more_namespace(head));
+	tomoyo_read_unlock(idx);
 	len = head->read_user_buf - buffer;
 	mutex_unlock(&head->io_sem);
 	return len;
@@ -2071,8 +2069,6 @@ static int tomoyo_parse_policy(struct tomoyo_io_buffer *head, char *line)
  * @buffer_len: Size of @buffer.
  *
  * Returns @buffer_len on success, negative value otherwise.
- *
- * Caller holds tomoyo_read_lock().
  */
 int tomoyo_write_control(struct tomoyo_io_buffer *head,
 			 const char __user *buffer, const int buffer_len)
@@ -2080,12 +2076,14 @@ int tomoyo_write_control(struct tomoyo_io_buffer *head,
 	int error = buffer_len;
 	size_t avail_len = buffer_len;
 	char *cp0 = head->write_buf;
+	int idx;
 	if (!head->write)
 		return -ENOSYS;
 	if (!access_ok(VERIFY_READ, buffer, buffer_len))
 		return -EFAULT;
 	if (mutex_lock_interruptible(&head->io_sem))
 		return -EINTR;
+	idx = tomoyo_read_lock();
 	/* Read a line and dispatch it to the policy handler. */
 	while (avail_len > 0) {
 		char c;
@@ -2148,6 +2146,7 @@ int tomoyo_write_control(struct tomoyo_io_buffer *head,
 		}
 	}
 out:
+	tomoyo_read_unlock(idx);
 	mutex_unlock(&head->io_sem);
 	return error;
 }
@@ -2157,30 +2156,18 @@ int tomoyo_write_control(struct tomoyo_io_buffer *head,
  *
  * @head: Pointer to "struct tomoyo_io_buffer".
  *
- * Releases memory and returns 0.
- *
- * Caller looses tomoyo_read_lock().
+ * Returns 0.
  */
 int tomoyo_close_control(struct tomoyo_io_buffer *head)
 {
-	const bool is_write = !!head->write_buf;
-
 	/*
 	 * If the file is /sys/kernel/security/tomoyo/query , decrement the
 	 * observer counter.
 	 */
-	if (head->type == TOMOYO_QUERY)
-		atomic_dec(&tomoyo_query_observers);
-	else if (head->type != TOMOYO_AUDIT)
-		tomoyo_read_unlock(head->reader_idx);
-	/* Release memory used for policy I/O. */
-	kfree(head->read_buf);
-	head->read_buf = NULL;
-	kfree(head->write_buf);
-	head->write_buf = NULL;
-	kfree(head);
-	if (is_write)
-		tomoyo_run_gc();
+	if (head->type == TOMOYO_QUERY &&
+	    atomic_dec_and_test(&tomoyo_query_observers))
+		wake_up_all(&tomoyo_answer_wait);
+	tomoyo_notify_gc(head, false);
 	return 0;
 }
 

security/tomoyo/common.h

@@ -441,8 +441,6 @@ struct tomoyo_io_buffer {
 	int (*poll) (struct file *file, poll_table *wait);
 	/* Exclusive lock for this structure.   */
 	struct mutex io_sem;
-	/* Index returned by tomoyo_read_lock(). */
-	int reader_idx;
 	char __user *read_user_buf;
 	int read_user_buf_avail;
 	struct {
@@ -480,6 +478,10 @@ struct tomoyo_io_buffer {
 	int writebuf_size;
 	/* Type of this interface.              */
 	u8 type;
+	/* Users counter protected by tomoyo_io_buffer_list_lock. */
+	u8 users;
+	/* List for telling GC not to kfree() elements. */
+	struct list_head list;
 };
 
 /*
@@ -651,7 +653,7 @@ int tomoyo_find_next_domain(struct linux_binprm *bprm);
 void tomoyo_print_ulong(char *buffer, const int buffer_len,
 			const unsigned long value, const u8 type);
 void tomoyo_put_name_union(struct tomoyo_name_union *ptr);
-void tomoyo_run_gc(void);
+void tomoyo_notify_gc(struct tomoyo_io_buffer *head, const bool is_register);
 void tomoyo_memory_free(void *ptr);
 int tomoyo_update_domain(struct tomoyo_acl_info *new_entry, const int size,
 			 struct tomoyo_acl_param *param,

security/tomoyo/gc.c

@@ -11,13 +11,123 @@
 #include <linux/kthread.h>
 #include <linux/slab.h>
 
+/* The list for "struct tomoyo_io_buffer". */
+static LIST_HEAD(tomoyo_io_buffer_list);
+/* Lock for protecting tomoyo_io_buffer_list. */
+static DEFINE_SPINLOCK(tomoyo_io_buffer_list_lock);
+
+/* Size of an element. */
+static const u8 tomoyo_element_size[TOMOYO_MAX_POLICY] = {
+	[TOMOYO_ID_GROUP] = sizeof(struct tomoyo_group),
+	[TOMOYO_ID_PATH_GROUP] = sizeof(struct tomoyo_path_group),
+	[TOMOYO_ID_NUMBER_GROUP] = sizeof(struct tomoyo_number_group),
+	[TOMOYO_ID_AGGREGATOR] = sizeof(struct tomoyo_aggregator),
+	[TOMOYO_ID_TRANSITION_CONTROL] =
+	sizeof(struct tomoyo_transition_control),
+	[TOMOYO_ID_MANAGER] = sizeof(struct tomoyo_manager),
+	/* [TOMOYO_ID_NAME] = "struct tomoyo_name"->size, */
+	/* [TOMOYO_ID_ACL] =
+	   tomoyo_acl_size["struct tomoyo_acl_info"->type], */
+	[TOMOYO_ID_DOMAIN] = sizeof(struct tomoyo_domain_info),
+};
+
+/* Size of a domain ACL element. */
+static const u8 tomoyo_acl_size[] = {
+	[TOMOYO_TYPE_PATH_ACL] = sizeof(struct tomoyo_path_acl),
+	[TOMOYO_TYPE_PATH2_ACL] = sizeof(struct tomoyo_path2_acl),
+	[TOMOYO_TYPE_PATH_NUMBER_ACL] = sizeof(struct tomoyo_path_number_acl),
+	[TOMOYO_TYPE_MKDEV_ACL] = sizeof(struct tomoyo_mkdev_acl),
+	[TOMOYO_TYPE_MOUNT_ACL] = sizeof(struct tomoyo_mount_acl),
+};
+
+/**
+ * tomoyo_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/tomoyo/ users or not.
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true if @element is used by /sys/kernel/security/tomoyo/ users,
+ * false otherwise.
+ */
+static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
+{
+	struct tomoyo_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
+		head->users++;
+		spin_unlock(&tomoyo_io_buffer_list_lock);
+		if (mutex_lock_interruptible(&head->io_sem)) {
+			in_use = true;
+			goto out;
+		}
+		if (head->r.domain == element || head->r.group == element ||
+		    head->r.acl == element || &head->w.domain->list == element)
+			in_use = true;
+		mutex_unlock(&head->io_sem);
+out:
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	return in_use;
+}
+
+/**
+ * tomoyo_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/tomoyo/ users or not.
+ *
+ * @string: String to check.
+ * @size:   Memory allocated for @string .
+ *
+ * Returns true if @string is used by /sys/kernel/security/tomoyo/ users,
+ * false otherwise.
+ */
+static bool tomoyo_name_used_by_io_buffer(const char *string,
+					  const size_t size)
+{
+	struct tomoyo_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
+		int i;
+		head->users++;
+		spin_unlock(&tomoyo_io_buffer_list_lock);
+		if (mutex_lock_interruptible(&head->io_sem)) {
+			in_use = true;
+			goto out;
+		}
+		for (i = 0; i < TOMOYO_MAX_IO_READ_QUEUE; i++) {
+			const char *w = head->r.w[i];
+			if (w < string || w > string + size)
+				continue;
+			in_use = true;
+			break;
+		}
+		mutex_unlock(&head->io_sem);
+out:
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	return in_use;
+}
+
+/* Structure for garbage collection. */
 struct tomoyo_gc {
 	struct list_head list;
 	enum tomoyo_policy_id type;
+	size_t size;
 	struct list_head *element;
 };
-static LIST_HEAD(tomoyo_gc_queue);
-static DEFINE_MUTEX(tomoyo_gc_mutex);
+/* List of entries to be deleted. */
+static LIST_HEAD(tomoyo_gc_list);
+/* Length of tomoyo_gc_list. */
+static int tomoyo_gc_list_len;
 
 /**
  * tomoyo_add_to_gc - Add an entry to to be deleted list.
@@ -43,10 +153,42 @@ static bool tomoyo_add_to_gc(const int type, struct list_head *element)
 	if (!entry)
 		return false;
 	entry->type = type;
+	if (type == TOMOYO_ID_ACL)
+		entry->size = tomoyo_acl_size[
+			      container_of(element,
+					   typeof(struct tomoyo_acl_info),
+					   list)->type];
+	else if (type == TOMOYO_ID_NAME)
+		entry->size = strlen(container_of(element,
+						  typeof(struct tomoyo_name),
+						  head.list)->entry.name) + 1;
+	else
+		entry->size = tomoyo_element_size[type];
 	entry->element = element;
-	list_add(&entry->list, &tomoyo_gc_queue);
+	list_add(&entry->list, &tomoyo_gc_list);
 	list_del_rcu(element);
-	return true;
+	return tomoyo_gc_list_len++ < 128;
+}
+
+/**
+ * tomoyo_element_linked_by_gc - Validate next element of an entry.
+ *
+ * @element: Pointer to an element.
+ * @size:    Size of @element in byte.
+ *
+ * Returns true if @element is linked by other elements in the garbage
+ * collector's queue, false otherwise.
+ */
+static bool tomoyo_element_linked_by_gc(const u8 *element, const size_t size)
+{
+	struct tomoyo_gc *p;
+	list_for_each_entry(p, &tomoyo_gc_list, list) {
+		const u8 *ptr = (const u8 *) p->element->next;
+		if (ptr < element || element + size < ptr)
+			continue;
+		return true;
+	}
+	return false;
 }
 
 /**
@@ -151,6 +293,13 @@ static void tomoyo_del_acl(struct list_head *element)
 	}
 }
 
+/**
+ * tomoyo_del_domain - Delete members in "struct tomoyo_domain_info".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true if deleted, false otherwise.
+ */
 static bool tomoyo_del_domain(struct list_head *element)
 {
 	struct tomoyo_domain_info *domain =
@@ -360,13 +509,44 @@ static void tomoyo_collect_entry(void)
 	mutex_unlock(&tomoyo_policy_lock);
 }
 
-static void tomoyo_kfree_entry(void)
+/**
+ * tomoyo_kfree_entry - Delete entries in tomoyo_gc_list.
+ *
+ * Returns true if some entries were kfree()d, false otherwise.
+ */
+static bool tomoyo_kfree_entry(void)
 {
 	struct tomoyo_gc *p;
 	struct tomoyo_gc *tmp;
+	bool result = false;
 
-	list_for_each_entry_safe(p, tmp, &tomoyo_gc_queue, list) {
+	list_for_each_entry_safe(p, tmp, &tomoyo_gc_list, list) {
 		struct list_head *element = p->element;
+
+		/*
+		 * list_del_rcu() in tomoyo_add_to_gc() guarantees that the
+		 * list element became no longer reachable from the list which
+		 * the element was originally on (e.g. tomoyo_domain_list).
+		 * Also, synchronize_srcu() in tomoyo_gc_thread() guarantees
+		 * that the list element became no longer referenced by syscall
+		 * users.
+		 *
+		 * However, there are three users which may still be using the
+		 * list element. We need to defer until all of these users
+		 * forget the list element.
+		 *
+		 * Firstly, defer until "struct tomoyo_io_buffer"->r.{domain,
+		 * group,acl} and "struct tomoyo_io_buffer"->w.domain forget
+		 * the list element.
+		 */
+		if (tomoyo_struct_used_by_io_buffer(element))
+			continue;
+		/*
+		 * Secondly, defer until all other elements in the
+		 * tomoyo_gc_list list forget the list element.
+		 */
+		if (tomoyo_element_linked_by_gc((const u8 *) element, p->size))
+			continue;
 		switch (p->type) {
 		case TOMOYO_ID_TRANSITION_CONTROL:
 			tomoyo_del_transition_control(element);
@@ -378,6 +558,14 @@ static void tomoyo_kfree_entry(void)
 			tomoyo_del_manager(element);
 			break;
 		case TOMOYO_ID_NAME:
+			/*
+			 * Thirdly, defer until all "struct tomoyo_io_buffer"
+			 * ->r.w[] forget the list element.
+			 */
+			if (tomoyo_name_used_by_io_buffer(
+			    container_of(element, typeof(struct tomoyo_name),
+					 head.list)->entry.name, p->size))
+				continue;
 			tomoyo_del_name(element);
 			break;
 		case TOMOYO_ID_ACL:
@@ -402,7 +590,10 @@ static void tomoyo_kfree_entry(void)
 		tomoyo_memory_free(element);
 		list_del(&p->list);
 		kfree(p);
+		tomoyo_gc_list_len--;
+		result = true;
 	}
+	return result;
 }
 
 /**
@@ -418,25 +609,70 @@ static void tomoyo_kfree_entry(void)
  */
 static int tomoyo_gc_thread(void *unused)
 {
+	/* Garbage collector thread is exclusive. */
+	static DEFINE_MUTEX(tomoyo_gc_mutex);
+	if (!mutex_trylock(&tomoyo_gc_mutex))
+		goto out;
 	daemonize("GC for TOMOYO");
-	if (mutex_trylock(&tomoyo_gc_mutex)) {
-		int i;
-		for (i = 0; i < 10; i++) {
-			tomoyo_collect_entry();
-			if (list_empty(&tomoyo_gc_queue))
-				break;
-			synchronize_srcu(&tomoyo_ss);
-			tomoyo_kfree_entry();
+	do {
+		tomoyo_collect_entry();
+		if (list_empty(&tomoyo_gc_list))
+			break;
+		synchronize_srcu(&tomoyo_ss);
+	} while (tomoyo_kfree_entry());
+	{
+		struct tomoyo_io_buffer *head;
+		struct tomoyo_io_buffer *tmp;
+
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		list_for_each_entry_safe(head, tmp, &tomoyo_io_buffer_list,
+					 list) {
+			if (head->users)
+				continue;
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
 		}
-		mutex_unlock(&tomoyo_gc_mutex);
+		spin_unlock(&tomoyo_io_buffer_list_lock);
 	}
-	do_exit(0);
+	mutex_unlock(&tomoyo_gc_mutex);
+out:
+	/* This acts as do_exit(0). */
+	return 0;
 }
 
-void tomoyo_run_gc(void)
+/**
+ * tomoyo_notify_gc - Register/unregister /sys/kernel/security/tomoyo/ users.
+ *
+ * @head:        Pointer to "struct tomoyo_io_buffer".
+ * @is_register: True if register, false if unregister.
+ *
+ * Returns nothing.
+ */
+void tomoyo_notify_gc(struct tomoyo_io_buffer *head, const bool is_register)
 {
-	struct task_struct *task = kthread_create(tomoyo_gc_thread, NULL,
-						  "GC for TOMOYO");
-	if (!IS_ERR(task))
-		wake_up_process(task);
+	bool is_write = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	if (is_register) {
+		head->users = 1;
+		list_add(&head->list, &tomoyo_io_buffer_list);
+	} else {
+		is_write = head->write_buf != NULL;
+		if (!--head->users) {
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
+		}
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	if (is_write) {
+		struct task_struct *task = kthread_create(tomoyo_gc_thread,
+							  NULL,
+							  "GC for TOMOYO");
+		if (!IS_ERR(task))
+			wake_up_process(task);
+	}
 }