lsm: add new securityfs delete function

When deleting a directory in the security file system, the existing
securityfs_remove requires the directory to be empty, otherwise
it will do nothing. This leads to a potential risk that the security
file system might be in an unclean state when the intended deletion
did not happen.

This commit introduces a new function securityfs_recursive_remove
to recursively delete a directory without leaving an unclean state.

Co-developed-by: Christian Brauner (Microsoft) <[e-mail]>
Signed-off-by: Fan Wu <[e-mail]>
[PM: subject line tweak]
Signed-off-by: Paul Moore <[e-mail]>

include/linux/security.h

···
 					 const char *target,
 					 const struct inode_operations *iops);
 extern void securityfs_remove(struct dentry *dentry);
+extern void securityfs_recursive_remove(struct dentry *dentry);
 
 #else /* CONFIG_SECURITYFS */
 

security/inode.c

···
 }
 EXPORT_SYMBOL_GPL(securityfs_remove);
 
+static void remove_one(struct dentry *victim)
+{
+	simple_release_fs(&mount, &mount_count);
+}
+
+/**
+ * securityfs_recursive_remove - recursively removes a file or directory
+ *
+ * @dentry: a pointer to a the dentry of the file or directory to be removed.
+ *
+ * This function recursively removes a file or directory in securityfs that was
+ * previously created with a call to another securityfs function (like
+ * securityfs_create_file() or variants thereof.)
+ */
+void securityfs_recursive_remove(struct dentry *dentry)
+{
+	if (IS_ERR_OR_NULL(dentry))
+		return;
+
+	simple_pin_fs(&fs_type, &mount, &mount_count);
+	simple_recursive_removal(dentry, remove_one);
+	simple_release_fs(&mount, &mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_recursive_remove);
+
 #ifdef CONFIG_SECURITY
 static struct dentry *lsm_dentry;
 static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,