Messages in this thread | | | Subject | Re: KMSAN: uninit-value in cdc_ncm_set_dgram_size | From | Oliver Neukum <> | Date | Tue, 05 Nov 2019 14:51:19 +0100 |
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Am Dienstag, den 05.11.2019, 13:25 +0100 schrieb Bjørn Mork: > Oliver Neukum <oneukum@suse.com> 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
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