[PATCH 05/25] fscrypt: new helper function - fscrypt_require_key()

[Eric Biggers]

From: Eric Biggers <ebiggers at google.com>

Add a helper function which checks if an inode is encrypted, and if so,
tries to set up its encryption key.  This is a pattern which is
duplicated in multiple places in each of ext4, f2fs, and ubifs --- for
example, when a regular file is asked to be opened or truncated.

Signed-off-by: Eric Biggers <ebiggers at google.com>
---
 include/linux/fscrypt_notsupp.h |  8 ++++++++
 include/linux/fscrypt_supp.h    | 28 ++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index 3f1325ec4646..3cfc953fef71 100644
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -174,4 +174,12 @@ static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
 	return -EOPNOTSUPP;
 }
 
+/* hooks.c */
+static inline int fscrypt_require_key(struct inode *inode)
+{
+	if (IS_ENCRYPTED(inode))
+		return -EOPNOTSUPP;
+	return 0;
+}
+
 #endif	/* _LINUX_FSCRYPT_NOTSUPP_H */
diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h
index 32e2fcf13b01..b6d4b5d303a3 100644
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -142,4 +142,32 @@ extern void fscrypt_pullback_bio_page(struct page **, bool);
 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 				 unsigned int);
 
+/* hooks.c */
+
+/**
+ * fscrypt_require_key - require an inode's encryption key
+ * @inode: the inode we need the key for
+ *
+ * If the inode is encrypted, set up its encryption key if not already done.
+ * Then require that the key be present and return -ENOKEY otherwise.
+ *
+ * No locks are needed, and currently the key will live as long as the struct
+ * inode --- so it won't go away from under you.
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ * if a problem occurred while setting up the encryption key.
+ */
+static inline int fscrypt_require_key(struct inode *inode)
+{
+	if (IS_ENCRYPTED(inode)) {
+		int err = fscrypt_get_encryption_info(inode);
+
+		if (err)
+			return err;
+		if (!fscrypt_has_encryption_key(inode))
+			return -ENOKEY;
+	}
+	return 0;
+}
+
 #endif	/* _LINUX_FSCRYPT_SUPP_H */
-- 
2.14.1.821.g8fa685d3b7-goog