3 files changed, 47 insertions, 0 deletions
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 9c9a53f99327..c422367baed9 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -204,4 +204,37 @@ static inline int fscrypt_prepare_link(struct dentry *old_dentry,
 	return 0;
 }
 
+/**
+ * fscrypt_prepare_rename - prepare for a rename between possibly-encrypted directories
+ * @old_dir: source directory
+ * @old_dentry: dentry for source file
+ * @new_dir: target directory
+ * @new_dentry: dentry for target location (may be negative unless exchanging)
+ * @flags: rename flags (we care at least about %RENAME_EXCHANGE)
+ *
+ * Prepare for ->rename() where the source and/or target directories may be
+ * encrypted.  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.  A rename to an existing name, on the other hand,
+ * *is* cryptographically possible without the key.  However, we take the more
+ * conservative approach and just forbid all no-key renames.
+ *
+ * We also verify that the rename will not violate the constraint that all files
+ * in an encrypted directory tree use the same encryption policy.
+ *
+ * Return: 0 on success, -ENOKEY if an encryption key is missing, -EPERM if the
+ * rename would cause inconsistent encryption policies, or another -errno code.
+ */
+static inline int fscrypt_prepare_rename(struct inode *old_dir,
+					 struct dentry *old_dentry,
+					 struct inode *new_dir,
+					 struct dentry *new_dentry,
+					 unsigned int flags)
+{
+	if (IS_ENCRYPTED(old_dir) || IS_ENCRYPTED(new_dir))
+		return __fscrypt_prepare_rename(old_dir, old_dentry,
+						new_dir, new_dentry, flags);
+	return 0;
+}
+
 #endif	/* _LINUX_FSCRYPT_H */
diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index d7d1039eb6b5..6af378d8126e 100644
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -192,4 +192,13 @@ static inline int __fscrypt_prepare_link(struct inode *inode,
 	return -EOPNOTSUPP;
 }
 
+static inline int __fscrypt_prepare_rename(struct inode *old_dir,
+					   struct dentry *old_dentry,
+					   struct inode *new_dir,
+					   struct dentry *new_dentry,
+					   unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif	/* _LINUX_FSCRYPT_NOTSUPP_H */
diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h
index 80706283da75..40f35073145f 100644
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -146,5 +146,10 @@ extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 /* hooks.c */
 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
 extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
+extern int __fscrypt_prepare_rename(struct inode *old_dir,
+				    struct dentry *old_dentry,
+				    struct inode *new_dir,
+				    struct dentry *new_dentry,
+				    unsigned int flags);
 
 #endif	/* _LINUX_FSCRYPT_SUPP_H */