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Ask the RNG to self-seed before generating a random number. #24

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May 17, 2016
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Ask the RNG to self-seed before generating a random number. #24

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1 change: 1 addition & 0 deletions lib/netif.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,7 @@ let err_partial_write len' page =

let connect devname =
try
Random.self_init ();
let fd, devname = Tuntap.opentap ~pi:false ~devname () in
let dev = Lwt_unix.of_unix_file_descr ~blocking:true fd in
let mac = Macaddr.make_local (fun _ -> Random.int 256) in
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@yomimono yomimono May 16, 2016

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On second thought, a completely random MAC is a bad idea. MAC addresses are structured and we should make sure that the globally-unique/link-local and unicast/multicast bits of the OUI are set as expected.

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@djs55 djs55 May 16, 2016

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FYI some MAC related stuff here:
https://github.com/xapi-project/xenopsd/blob/900f9ec3251fd9850a1326a3617a73639a10c01c/lib/mac.ml#L32

On Mon, May 16, 2016 at 4:31 PM, Mindy Preston notifications@github.com
wrote:

In lib/netif.ml
#24 (comment):

@@ -67,6 +67,7 @@ let err_partial_write len' page =

let connect devname =
try

  • Random.self_init ();
    let fd, devname = Tuntap.opentap ~pi:false ~devname () in
    let dev = Lwt_unix.of_unix_file_descr ~blocking:true fd in
    let mac = Macaddr.make_local (fun _ -> Random.int 256) in

On second thought, a completely random MAC is a bad idea. MAC addresses
are structured and we should make sure that the globally-unique/link-local
and unicast/multicast bits of the OUI are set as expected.

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https://github.com/mirage/mirage-net-unix/pull/24/files/b3aed3776ca65fbe6da916755292b6163d54c181#r63372705

Dave Scott

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@yomimono yomimono May 16, 2016 •
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It looks like Macaddr.make_local does the right thing here, so the patch as written should be OK: https://github.com/mirage/ocaml-ipaddr/blob/master/lib/macaddr.ml#L121

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@mato mato May 17, 2016

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@yomimono +1, Macaddr.make_local of random bits is fine.

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