Am Dienstag, den 05.11.2019, 13:25 +0100 schrieb Bjørn Mork: > Oliver Neukum <oneukum@xxxxxxxx> writes: > > Am Montag, den 04.11.2019, 22:22 +0100 schrieb Bjørn Mork: > Ah, OK. So that could be fixed with e.g. > > if (err < 2) > goto out; > > > Or would it be better to add a strict length checking variant of this > API? There are probably lots of similar cases where we expect a We would lose flexibilty and the check needs to be there anyway. > Right. And probably all 16 or 32 bit integer reads... > > Looking at the NCM spec, I see that the wording is annoyingly flexible > wrt length - both ways. E.g for GetNetAddress: > > To get the entire network address, the host should set wLength to at > least 6. The function shall never return more than 6 bytes in response > to this command. > > Maybe the correct fix is simply to let usbnet_read_cmd() initialize the > full buffer regardless of what the device returns? I.e. This issue has never been observed in the wild. We are defending against a possible attack. It is better to react drastically. > at do you think? > > Personally, I don't think it makes sense for a device to return a 1-byte > mtu or 3-byte mac address. But the spec allows it and this would at > least make it safe. Hence we should ignore such a reply. The support is optional anyway. For usbnet as such, however, we cannot really hardcode the size of a MAC. Regards Oliver
