fscrypt: new helper function - fscrypt_prepare_link()

Introduce a helper function which prepares to link an inode into a
possibly-encrypted directory.  It handles setting up the target
directory's encryption key, then verifying that the link won't violate
the constraint that all files in an encrypted directory tree use the
same encryption policy.

Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 069088e91ea9..8b90217320dd 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -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);