Hi, On Mon, Jul 18, 2016 at 3:01 PM, Oliver Neukum <oneu...@suse.com> wrote: > On Mon, 2016-07-18 at 14:24 +0200, Kristian Evensen wrote: >> The firmware in the ZTE MF823/831/910 modems/mifis use OS fingerprinting to >> determine which type of device to export. In addition, these devices export >> a REST API which can also be used to control the type of device. So far, on >> Linux, the devices have been seen as RNDIS or CDC Ether. >> >> When CDC Ether is used, devices of the same type are, as with RNDIS, >> exported with the same, bogus random MAC address. In addition, the devices > > Please explain. If the MAC is random, I fail to see why the host would > be any better at making up a MAC.
Sorry for not explaining this properly. The problem is that all devices of the same type store the same value in iMACAddress. On all MF831/MF910s (that I have seen) 36:4b:50:b7:ef:da is stored in this value, while 36:4b:50:b7:ef:38 is stored on MF823. In order to ensure that all devices on a host has a unique MAC-address, I think it is better to generate a new random MAC on the host than to trust the value returned from the device. >> * If a random MAC is read from device, then generate a new random MAC >> address. This fix will apply to all devices using cdc_ether, but that >> should be ok as we will also fix similar mistakes from other >> manufacturers. > > I am not really happy with this. > > If this is specific to the device a quirk should be used. If it is a > truly generic misdesign, it does not belong into cdc-ether. It should go > into the generic layer. We saw the same behaviour when these devices are exposed as RNDIS and decided to apply a generic fix instead of limiting ourself to for example the two, known bogus MAC address. See commit a5a18bdf7453d505783e40e47ebb84bfdd35f93b and the thread "[PATCH] rndis_host: Set random MAC for ZTE MF910" (http://www.spinics.net/lists/linux-usb/msg143727.html) for the discussion. However, I have no strong objections towards for example checking against the two bad MAC addresses before generating a random MAC. -Kristian
