f2fs crypto: handle unexpected lack of encryption keys

This patch syncs f2fs with commit abdd438b26b4 ("ext4 crypto: handle
unexpected lack of encryption keys") from ext4.

Fix up attempts by users to try to write to a file when they don't
have access to the encryption key.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 05f5f2f..8dea195 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -424,6 +424,8 @@
 		err = f2fs_get_encryption_info(inode);
 		if (err)
 			return 0;
+		if (!f2fs_encrypted_inode(inode))
+			return -ENOKEY;
 	}
 
 	/* we don't need to use inline_data strictly */
@@ -443,7 +445,9 @@
 	if (!ret && f2fs_encrypted_inode(inode)) {
 		ret = f2fs_get_encryption_info(inode);
 		if (ret)
-			ret = -EACCES;
+			return -EACCES;
+		if (!f2fs_encrypted_inode(inode))
+			return -ENOKEY;
 	}
 	return ret;
 }