cifs: check if SMB2 PDU size has been padded and suppress the warning

BugLink: https://bugs.launchpad.net/bugs/1797563

[ Upstream commit e6c47dd0 ]

Some SMB2/3 servers, Win2016 but possibly others too, adds padding
not only between PDUs in a compound but also to the final PDU.
This padding extends the PDU to a multiple of 8 bytes.

Check if the unexpected length looks like this might be the case
and avoid triggering the log messages for :

  "SMB2 server sent bad RFC1001 len %d not %d\n"
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/cifs/smb2misc.c

@@ -211,6 +211,13 @@ smb2_check_message(char *buf, unsigned int length, struct TCP_Server_Info *srvr)
 		if (clc_len == 4 + len + 1)
 			return 0;
 
+		/*
+		 * Some windows servers (win2016) will pad also the final
+		 * PDU in a compound to 8 bytes.
+		 */
+		if (((clc_len + 7) & ~7) == len)
+			return 0;
+
 		/*
 		 * MacOS server pads after SMB2.1 write response with 3 bytes
 		 * of junk. Other servers match RFC1001 len to actual