[PATCH] erofs: zero out when listxattr is called with no xattr

[Gao Xiang]

From: Gao Xiang <gaoxiang25 at huawei.com>

As David reported [1], ENODATA returns when attempting
to modify files by using EROFS as a overlayfs lower layer.

The root cause is that listxattr could return unexpected
-ENODATA by mistake for inodes without xattr. That breaks
listxattr return value convention and it can cause copy
up failure when used with overlayfs.

Resolve by zeroing out if no xattr is found for listxattr.

[1] https://lore.kernel.org/r/CAEvUa7nxnby+rxK-KRMA46=exeOMApkDMAV08AjMkkPnTPV4CQ@mail.gmail.com
Fixes: cadf1ccf1b00 ("staging: erofs: add error handling for xattr submodule")
Cc: <stable at vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---
 fs/erofs/xattr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index a13a78725c57..b766c3ee5fa8 100644
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -649,6 +649,8 @@ ssize_t erofs_listxattr(struct dentry *dentry,
 	struct listxattr_iter it;
 
 	ret = init_inode_xattrs(d_inode(dentry));
+	if (ret == -ENOATTR)
+		return 0;
 	if (ret)
 		return ret;
 
-- 
2.20.1