Date: Tue, 9 Apr 2019 13:19:24 -0700 From: John Baldwin <jhb@FreeBSD.org> To: rgrimes@freebsd.org Cc: Ian Lepore <ian@freebsd.org>, Ganbold Tsagaankhuu <ganbold@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r346052 - head/sys/dev/usb/net Message-ID: <8c5292c0-5464-8995-4518-181886201692@FreeBSD.org> In-Reply-To: <201904091948.x39JmBZk061857@gndrsh.dnsmgr.net> References: <201904091948.x39JmBZk061857@gndrsh.dnsmgr.net>
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On 4/9/19 12:48 PM, Rodney W. Grimes wrote: >> On 4/9/19 9:59 AM, Ian Lepore wrote: >>> On Tue, 2019-04-09 at 09:33 -0700, John Baldwin wrote: >>>> On 4/9/19 9:17 AM, Ian Lepore wrote: >>>>> On Tue, 2019-04-09 at 09:11 -0700, John Baldwin wrote: >>>>>> On 4/9/19 6:54 AM, Ganbold Tsagaankhuu wrote: >>>>>>> Author: ganbold >>>>>>> Date: Tue Apr 9 13:54:08 2019 >>>>>>> New Revision: 346052 >>>>>>> URL: https://svnweb.freebsd.org/changeset/base/346052 >>>>>>> >>>>>>> Log: >>>>>>> In some cases like NanoPI R1, its second USB ethernet >>>>>>> RTL8152 (chip version URE_CHIP_VER_4C10) doesn't >>>>>>> have hardwired MAC address, in other words, it is all zeros. >>>>>>> This commit fixes it by setting random MAC address >>>>>>> when MAC address is all zeros. >>>>>>> >>>>>>> Reviewed by: kevlo >>>>>>> Differential Revision: >>>>>>> https://reviews.freebsd.org/D19856 >>>>>> >>>>>> It would be best to not use a purely random mac address and to >>>>>> use >>>>>> the >>>>>> function kevans@ added recently. That function generates a MAC >>>>>> address >>>>>> from the FreeBSD OUI using a cryptographic hash so you get a >>>>>> stable address across boots on a given host. >>>>>> >>>>> >>>>> How could that possibly work? If it's not random, you can't have >>>>> two >>>>> such devices on the same network. If it is random, it's not stable >>>>> from one boot to the next. >>>> >>>> It uses the UUID and interface name as input into the hash. >>> >>>> The UUID is per-host. >>> >>> Oh, so it only works on x86 (or I guess any system that has something >>> like a bios that can provide you with a uuid that doesn't change from >>> one boot to the next). >> >> The function is in one centralized place where you are free to add other >> data as input into the hash. We do always generate a uuid that we save >> on boot if we aren't seeded with one by firmware, though that is probably >> too late for this driver (so +1 may in fact be a better route). It should >> be fine for psuedo interfaces created post-boot though even on non-x86 due >> to /etc/rc.d/hostid. Pure random MAC's are not really great either. > > Cant the loader load /etc/rc.d/hostid and put it in something that > the kernel could get at, or a module written that handles this? It's a different file, and yes in theory the loader could look at the file and set UUID and hostid env vars. However, that's a no-op for most use cases. If other platforms have some kind of firmware-provided thing that isn't a UUID, it would be good to teach the centralized function about those as an input to the hash, but at least that can be done in place rather than having open-coded MAC generators in various drivers. -- John Baldwin
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