[PATCH 4.16 209/279] cifs: smb2ops: Fix listxattr() when there are no EAs

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paulo Alcantara <palcantara@xxxxxxx>

[ Upstream commit ae2cd7fb478b8da707906ee1706ae1379968a8f9 ]

As per listxattr(2):

       On success, a nonnegative number is returned indicating the size
       of the extended attribute name list.  On failure, -1 is returned
       and errno  is set appropriately.

In SMB1, when the server returns an empty EA list through a listxattr(),
it will correctly return 0 as there are no EAs for the given file.

However, in SMB2+, it returns -ENODATA in listxattr() which is wrong since
the request and response were sent successfully, although there's no actual
EA for the given file.

This patch fixes listxattr() for SMB2+ by returning 0 in cifs_listxattr()
when the server returns an empty list of EAs.

Signed-off-by: Paulo Alcantara <palcantara@xxxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
Signed-off-by: Steve French <smfrench@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/cifs/smb2ops.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -589,9 +589,15 @@ smb2_query_eas(const unsigned int xid, s
 
 	SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 
+	/*
+	 * If ea_name is NULL (listxattr) and there are no EAs, return 0 as it's
+	 * not an error. Otherwise, the specified ea_name was not found.
+	 */
 	if (!rc)
 		rc = move_smb2_ea_to_cifs(ea_data, buf_size, smb2_data,
 					  SMB2_MAX_EA_BUF, ea_name);
+	else if (!ea_name && rc == -ENODATA)
+		rc = 0;
 
 	kfree(smb2_data);
 	return rc;