cifs: print warning mounting with vers=1.0

We really, really don't want people using insecure dialects
unless they realize what they are doing ...

Add mount warning if mounting with vers=1.0 (older SMB1/CIFS
dialect) instead of the default (SMB2.1 or later, typically
SMB3.1.1).
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Acked-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/connect.c

@@ -1471,6 +1471,9 @@ cifs_parse_smb_version(char *value, struct smb_vol *vol, bool is_smb3)
 			cifs_dbg(VFS, "vers=1.0 (cifs) not permitted when mounting with smb3\n");
 			return 1;
 		}
+		cifs_dbg(VFS, "Use of the less secure dialect vers=1.0 "
+			   "is not recommended unless required for "
+			   "access to very old servers\n");
 		vol->ops = &smb1_operations;
 		vol->vals = &smb1_values;
 		break;