Add fido(4), a HID driver for FIDO/U2F security keys

While FIDO/U2F keys were already supported by the generic uhid(4)
driver, this driver adds the first step to tighten the security of
FIDO/U2F access.  Specifically, users don't need read/write access to
all USB/HID devices anymore and the driver also improves integration
with pledge(2) and unveil(2): It is pledge-friendly because it doesn't
require any ioctls to discover the device and unveil-friendly because
it uses a single /dev/fido/* directory for its device nodes.

It also allows to support FIDO/U2F in firefox without further
weakening the "sandbox" of the browser.  Firefox does not have a
proper privsep design and many operations, such as U2F access, are
handled directly by the main process.  This means that the browser's
"fat" main process needs direct read/write access to all USB HID
devices, at least on other operating systems.  With fido(4) we can
support security keys in Firefox under OpenBSD without such a
compromise.

With this change, libfido2 stops using the ioctl to query the device
vendor/product and just assumes "OpenBSD" "fido(4)" instead.  The
ioctl is still supported but there was no benefit in obtaining the
vendor product or name; it also allows to use libfido2 under pledge.

With feedback from deraadt@ and many others
OK kettenis@ djm@ and jmc@ for the manpage bits

1 files changed, 2 insertions, 1 deletions

diff --git a/etc/etc.amd64/MAKEDEV.md b/etc/etc.amd64/MAKEDEV.md
index c2a2c83b529..f46b52bd7d6 100644
--- a/etc/etc.amd64/MAKEDEV.md
+++ b/etc/etc.amd64/MAKEDEV.md
@@ -1,6 +1,6 @@
 define(MACHINE,amd64)dnl
 vers(__file__,
-	{-$OpenBSD: MAKEDEV.md,v 1.71 2019/12/13 21:03:57 deraadt Exp $-},
+	{-$OpenBSD: MAKEDEV.md,v 1.72 2019/12/17 13:08:54 reyk Exp $-},
 etc.MACHINE)dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
@@ -59,6 +59,7 @@ _DEV(ttyU, 66)
 _DEV(uall)
 _DEV(ugen, 63)
 _DEV(uhid, 62)
+_DEV(fido, 98)
 _DEV(ulpt, 64)
 _DEV(usb, 61)
 _TITLE(spec)