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SubjectRe: Get physical MAC address
Date
On Jan 01, 2008, at 21:42:18, Jon Masters wrote:
> On Mon, 2007-12-31 at 12:39 +0700, Theewara Vorakosit wrote:
>> I get MAC address from ioctl. However, ifconfig can change this
>> MAC address. Can I get a real physical MAC address of the NIC?
>
> Forgive me reading into your mail...this smells a bit like some
> kind of licensing/compliance thing. Just bear in mind that using
> the MAC to verify the identity of a machine is utterly useless and
> pointless - anyone can trivially fool your software[0] to see what
> it "wants".

Not necessarily; I can easily see distros wanting to have a "Restore
defaults" button in their network config windows which also includes
restoring the default MAC address to the NIC. It should also be
pointed out that anybody with one of a selection of re-flashable NICS
(or NICS with removable EEPROMS) can easily change the MAC address on
their NIC. Other alternatives includes renaming eth0 to mynet0 and
creating a downed dummy interface called "eth0" with the desired MAC
addr.


> [0] We used to have to do far worse kludgery in college, in order
> to prevent the silly powers that be who "banned" network cards
> other than those made by one manufacturer from being used on their
> little network.

Well for basically any userspace-level check, all it takes is
somebody who knows ASM and has about 5 minutes to track down the
problematic branch instructions. Then they just have to write a 10-
line GDB script which starts the program, traps the appropriate
instructions, and then changes a "0" to a "1" (or vice versa) before
the conditional branch. On Windows it's vaguely practical (albeit
crash-prone) to load a kernel hack which prevents your program from
being debugged, but under Linux it's effectively impossible

Cheers,
Kyle Moffett



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