f2fs crypto: handle unexpected lack of encryption keys

This patch syncs f2fs with commit abdd438b ("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: NTheodore Ts'o <tytso@mit.edu>
Signed-off-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/crypto_policy.c

@@ -192,7 +192,8 @@ int f2fs_inherit_context(struct inode *parent, struct inode *child,
 		return res;
 
 	ci = F2FS_I(parent)->i_crypt_info;
-	BUG_ON(ci == NULL);
+	if (ci == NULL)
+		return -ENOKEY;
 
 	ctx.format = F2FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 

fs/f2fs/file.c

@@ -424,6 +424,8 @@ static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 		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 @@ static int f2fs_file_open(struct inode *inode, struct file *filp)
 	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;
 }