[PATCH 07/25] fscrypt: new helper function - fscrypt_prepare_link()

@@ -47,3 +47,18 @@ int fscrypt_file_open(struct inode *inode, struct file *filp)
 	return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_file_open);
+
+int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
+{
+	int err;
+
+	err = fscrypt_require_key(dir);
+	if (err)
+		return err;
+
+	if (!fscrypt_has_permitted_context(dir, inode))
+		return -EPERM;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);

@@ -189,4 +189,13 @@ static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+static inline int fscrypt_prepare_link(struct dentry *old_dentry,
+				       struct inode *dir,
+				       struct dentry *dentry)
+{
+	if (IS_ENCRYPTED(dir))
+		return -EOPNOTSUPP;
+	return 0;
+}
+
 #endif	/* _LINUX_FSCRYPT_NOTSUPP_H */

@@ -172,4 +172,33 @@ static inline int fscrypt_require_key(struct inode *inode)
 
 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
 
+extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
+
+/**
+ * fscrypt_prepare_link - prepare to link an inode into a possibly-encrypted directory
+ * @old_dentry: an existing dentry for the inode being linked
+ * @dir: the target directory
+ * @dentry: negative dentry for the target filename
+ *
+ * A new link can only be added to an encrypted directory if the directory's
+ * encryption key is available --- since otherwise we'd have no way to encrypt
+ * the filename.  Therefore, we first set up the directory's encryption key (if
+ * not already done) and return an error if it's unavailable.
+ *
+ * We also verify that the link will not violate the constraint that all files
+ * in an encrypted directory tree use the same encryption policy.
+ *
+ * Return: 0 on success, -ENOKEY if the directory's encryption key is missing,
+ * -EPERM if the link would result in an inconsistent encryption policy, or
+ * another -errno code.
+ */
+static inline int fscrypt_prepare_link(struct dentry *old_dentry,
+				       struct inode *dir,
+				       struct dentry *dentry)
+{
+	if (IS_ENCRYPTED(dir))
+		return __fscrypt_prepare_link(d_inode(old_dentry), dir);
+	return 0;
+}
+
 #endif	/* _LINUX_FSCRYPT_SUPP_H */