securityfs: fix object creation races

inode needs to be fully set up before we feed it to d_instantiate().
securityfs_create_file() does *not* do so; it sets ->i_fop and
->i_private only after we'd exposed the inode.  Unfortunately,
that's done fairly deep in call chain, so the amount of churn
is considerable.  Helper functions killed by substituting into
their solitary call sites, dead code removed.  We finally can
bury default_file_ops, now that the final value of ->i_fop is
available (and assigned) at the point where inode is allocated.
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

security/inode.c

@@ -25,100 +25,6 @@
 static struct vfsmount *mount;
 static int mount_count;
 
-/*
- * TODO:
- *   I think I can get rid of these default_file_ops, but not quite sure...
- */
-static ssize_t default_read_file(struct file *file, char __user *buf,
-				 size_t count, loff_t *ppos)
-{
-	return 0;
-}
-
-static ssize_t default_write_file(struct file *file, const char __user *buf,
-				   size_t count, loff_t *ppos)
-{
-	return count;
-}
-
-static int default_open(struct inode *inode, struct file *file)
-{
-	if (inode->i_private)
-		file->private_data = inode->i_private;
-
-	return 0;
-}
-
-static const struct file_operations default_file_ops = {
-	.read =		default_read_file,
-	.write =	default_write_file,
-	.open =		default_open,
-	.llseek =	noop_llseek,
-};
-
-static struct inode *get_inode(struct super_block *sb, umode_t mode, dev_t dev)
-{
-	struct inode *inode = new_inode(sb);
-
-	if (inode) {
-		inode->i_ino = get_next_ino();
-		inode->i_mode = mode;
-		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-		switch (mode & S_IFMT) {
-		default:
-			init_special_inode(inode, mode, dev);
-			break;
-		case S_IFREG:
-			inode->i_fop = &default_file_ops;
-			break;
-		case S_IFDIR:
-			inode->i_op = &simple_dir_inode_operations;
-			inode->i_fop = &simple_dir_operations;
-
-			/* directory inodes start off with i_nlink == 2 (for "." entry) */
-			inc_nlink(inode);
-			break;
-		}
-	}
-	return inode;
-}
-
-/* SMP-safe */
-static int mknod(struct inode *dir, struct dentry *dentry,
-			 umode_t mode, dev_t dev)
-{
-	struct inode *inode;
-	int error = -ENOMEM;
-
-	if (dentry->d_inode)
-		return -EEXIST;
-
-	inode = get_inode(dir->i_sb, mode, dev);
-	if (inode) {
-		d_instantiate(dentry, inode);
-		dget(dentry);
-		error = 0;
-	}
-	return error;
-}
-
-static int mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
-{
-	int res;
-
-	mode = (mode & (S_IRWXUGO | S_ISVTX)) | S_IFDIR;
-	res = mknod(dir, dentry, mode, 0);
-	if (!res)
-		inc_nlink(dir);
-	return res;
-}
-
-static int create(struct inode *dir, struct dentry *dentry, umode_t mode)
-{
-	mode = (mode & S_IALLUGO) | S_IFREG;
-	return mknod(dir, dentry, mode, 0);
-}
-
 static inline int positive(struct dentry *dentry)
 {
 	return dentry->d_inode && !d_unhashed(dentry);
@@ -145,38 +51,6 @@ static struct file_system_type fs_type = {
 	.kill_sb =	kill_litter_super,
 };
 
-static int create_by_name(const char *name, umode_t mode,
-			  struct dentry *parent,
-			  struct dentry **dentry)
-{
-	int error = 0;
-
-	*dentry = NULL;
-
-	/* If the parent is not specified, we create it in the root.
-	 * We need the root dentry to do this, which is in the super
-	 * block. A pointer to that is in the struct vfsmount that we
-	 * have around.
-	 */
-	if (!parent)
-		parent = mount->mnt_root;
-
-	mutex_lock(&parent->d_inode->i_mutex);
-	*dentry = lookup_one_len(name, parent, strlen(name));
-	if (!IS_ERR(*dentry)) {
-		if (S_ISDIR(mode))
-			error = mkdir(parent->d_inode, *dentry, mode);
-		else
-			error = create(parent->d_inode, *dentry, mode);
-		if (error)
-			dput(*dentry);
-	} else
-		error = PTR_ERR(*dentry);
-	mutex_unlock(&parent->d_inode->i_mutex);
-
-	return error;
-}
-
 /**
  * securityfs_create_file - create a file in the securityfs filesystem
  *
@@ -209,31 +83,66 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
 				   struct dentry *parent, void *data,
 				   const struct file_operations *fops)
 {
-	struct dentry *dentry = NULL;
+	struct dentry *dentry;
+	int is_dir = S_ISDIR(mode);
+	struct inode *dir, *inode;
 	int error;
 
+	if (!is_dir) {
+		BUG_ON(!fops);
+		mode = (mode & S_IALLUGO) | S_IFREG;
+	}
+
 	pr_debug("securityfs: creating file '%s'\n",name);
 
 	error = simple_pin_fs(&fs_type, &mount, &mount_count);
-	if (error) {
-		dentry = ERR_PTR(error);
-		goto exit;
+	if (error)
+		return ERR_PTR(error);
+
+	if (!parent)
+		parent = mount->mnt_root;
+
+	dir = parent->d_inode;
+
+	mutex_lock(&dir->i_mutex);
+	dentry = lookup_one_len(name, parent, strlen(name));
+	if (IS_ERR(dentry))
+		goto out;
+
+	if (dentry->d_inode) {
+		error = -EEXIST;
+		goto out1;
 	}
 
-	error = create_by_name(name, mode, parent, &dentry);
-	if (error) {
-		dentry = ERR_PTR(error);
-		simple_release_fs(&mount, &mount_count);
-		goto exit;
+	inode = new_inode(dir->i_sb);
+	if (!inode) {
+		error = -ENOMEM;
+		goto out1;
 	}
 
-	if (dentry->d_inode) {
-		if (fops)
-			dentry->d_inode->i_fop = fops;
-		if (data)
-			dentry->d_inode->i_private = data;
+	inode->i_ino = get_next_ino();
+	inode->i_mode = mode;
+	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+	inode->i_private = data;
+	if (is_dir) {
+		inode->i_op = &simple_dir_inode_operations;
+		inode->i_fop = &simple_dir_operations;
+		inc_nlink(inode);
+		inc_nlink(dir);
+	} else {
+		inode->i_fop = fops;
 	}
-exit:
+	d_instantiate(dentry, inode);
+	dget(dentry);
+	mutex_unlock(&dir->i_mutex);
+	return dentry;
+
+out1:
+	dput(dentry);
+	dentry = ERR_PTR(error);
+out:
+	mutex_unlock(&dir->i_mutex);
+	simple_release_fs(&mount, &mount_count);
 	return dentry;
 }
 EXPORT_SYMBOL_GPL(securityfs_create_file);