"NetworkManagerUtils.h" contains a bunch of helper tools for core
daemon ("src/").
Unfortunately, it has dependencies to other parts of core,
such as "nm-device.h" and "nm-platform.h". Split out a part
of tools that are independent so that they can be used without
dragging in other dependencies.
"nm-core-utils.h" should only use libnm-core, "nm-logging.h"
and shared.
"NetworkManagerUtils.h" should provide all "nm-core-utils.h" and
possibly other utilities that have larger dependencies.
- All internal source files (except "examples", which are not internal)
should include "config.h" first. As also all internal source
files should include "nm-default.h", let "config.h" be included
by "nm-default.h" and include "nm-default.h" as first in every
source file.
We already wanted to include "nm-default.h" before other headers
because it might contains some fixes (like "nm-glib.h" compatibility)
that is required first.
- After including "nm-default.h", we optinally allow for including the
corresponding header file for the source file at hand. The idea
is to ensure that each header file is self contained.
- Don't include "config.h" or "nm-default.h" in any header file
(except "nm-sd-adapt.h"). Public headers anyway must not include
these headers, and internal headers are never included after
"nm-default.h", as of the first previous point.
- Include all internal headers with quotes instead of angle brackets.
In practice it doesn't matter, because in our public headers we must
include other headers with angle brackets. As we use our public
headers also to compile our interal source files, effectively the
result must be the same. Still do it for consistency.
- Except for <config.h> itself. Include it with angle brackets as suggested by
https://www.gnu.org/software/autoconf/manual/autoconf.html#Configuration-Headers
RFC7217 introduces an alternative mechanism for creating addresses during
stateless IPv6 address configuration. It's supposed to create addresses whose
host part stays stable in a particular network but changes when the hosts
enters another network to mitigate possibility of tracking the host movement.
It can be used alongside RFC 4941 privacy extensions (temporary addresses)
and replaces the use of RFC 4862 interface identifiers.
The address creation mode is controlld by ip6.addr_gen_mode property
(ADDR_GEN_MODE in ifcfg-rh), with values of "stable-privacy" and "eui-64",
defaulting to "eui-64" if unspecified.
The host part of an address is computed by hashing a system-specific secret
salted with various stable values that identify the connection with a secure
hash algorithm:
RID = F(Prefix, Net_Iface, Network_ID, DAD_Counter, secret_key)
For NetworkManager we use these parameters:
* F()
SHA256 hash function.
* Prefix
This is a network part of the /64 address
* Net_Iface
We use the interface name (e.g. "eth0"). This ensures the address won't
change with the change of interface hardware.
* Network_ID
We use the connection UUID here. This ensures the salt is different for
wireless networks with a different SSID as suggested by RFC7217.
* DAD_Counter
A per-address counter that increases with each DAD failure.
* secret_key
We store the secret key in /var/lib/NetworkManager/secret_key. If it's
shorter than 128 bits then it's rejected. If the file is not present we
initialize it by fetching 256 pseudo-random bits from /dev/urandom on
first use.
Duplicate address detection uses IDGEN_RETRIES = 3 and does not utilize the
IDGEN_DELAY delay (despite it SHOULD). This is for ease of implementation
and may change in future. Neither parameter is currently configurable.
