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Pull request 2096: 4923 gopacket dhcp vol.5
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Updates AdguardTeam#4923.

Squashed commit of the following:

commit 762a3f9
Merge: 2af65b4 34a34dc
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Dec 12 11:13:21 2023 +0300

    Merge branch 'master' into 4923-gopacket-dhcp-vol.5

commit 2af65b4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Dec 8 16:22:51 2023 +0300

    dhcpsvc: imp code

commit 71233b9
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Dec 8 15:26:25 2023 +0300

    dhcpsvc: imp docs

commit 2949544
Merge: 593e9ed 214175e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Dec 7 16:48:18 2023 +0300

    Merge branch 'master' into 4923-gopacket-dhcp-vol.5

commit 593e9ed
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Dec 7 16:45:10 2023 +0300

    dhcpsvc: imp docs

commit cdb1915
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Dec 7 16:33:56 2023 +0300

    dhcpsvc: imp code

commit a0c423c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Dec 5 20:56:43 2023 +0300

    dnspsvc: add opts

commit 050ab7f
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Dec 5 20:17:37 2023 +0300

    WIP
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@EugeneOne1
EugeneOne1 committed Dec 12, 2023
1 parent 34a34dc commit 79d7a1e
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215 changes: 211 additions & 4 deletions internal/dhcpsvc/v4.go
View file
Expand Up @@ -6,7 +6,10 @@ import (
"net/netip"
"time"

"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/golibs/netutil"
"github.com/google/gopacket/layers"
"golang.org/x/exp/slices"
)

// IPv4Config is the interface-specific configuration for DHCPv4.
Expand All @@ -26,7 +29,9 @@ type IPv4Config struct {
// RangeEnd is the last address in the range to assign to DHCP clients.
RangeEnd netip.Addr

// Options is the list of DHCP options to send to DHCP clients.
// Options is the list of DHCP options to send to DHCP clients. The options
// having a zero value within the Length field are treated as deletions of
// the corresponding options, either implicit or explicit.
Options layers.DHCPOptions

// LeaseDuration is the TTL of a DHCP lease.
Expand Down Expand Up @@ -73,7 +78,14 @@ type iface4 struct {
// name is the name of the interface.
name string

// TODO(e.burkov): Add options.
// implicitOpts are the options listed in Appendix A of RFC 2131 and
// initialized with default values. It must not have intersections with
// explicitOpts.
implicitOpts layers.DHCPOptions

// explicitOpts are the user-configured options. It must not have
// intersections with implicitOpts.
explicitOpts layers.DHCPOptions

// leaseTTL is the time-to-live of dynamic leases on this interface.
leaseTTL time.Duration
Expand Down Expand Up @@ -103,11 +115,206 @@ func newIface4(name string, conf *IPv4Config) (i *iface4, err error) {
return nil, fmt.Errorf("gateway ip %s in the ip range %s", conf.GatewayIP, addrSpace)
}

return &iface4{
i = &iface4{
name: name,
gateway: conf.GatewayIP,
subnet: subnet,
addrSpace: addrSpace,
leaseTTL: conf.LeaseDuration,
}, nil
}
i.implicitOpts, i.explicitOpts = conf.options()

return i, nil
}

// options returns the implicit and explicit options for the interface. The two
// lists are disjoint and the implicit options are initialized with default
// values.
//
// TODO(e.burkov): DRY with the IPv6 version.
func (conf *IPv4Config) options() (implicit, explicit layers.DHCPOptions) {
// Set default values of host configuration parameters listed in Appendix A
// of RFC-2131.
implicit = layers.DHCPOptions{
// Values From Configuration

layers.NewDHCPOption(layers.DHCPOptSubnetMask, conf.SubnetMask.AsSlice()),
layers.NewDHCPOption(layers.DHCPOptRouter, conf.GatewayIP.AsSlice()),

// IP-Layer Per Host

// An Internet host that includes embedded gateway code MUST have a
// configuration switch to disable the gateway function, and this switch
// MUST default to the non-gateway mode.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.5.
layers.NewDHCPOption(layers.DHCPOptIPForwarding, []byte{0x0}),

// A host that supports non-local source-routing MUST have a
// configurable switch to disable forwarding, and this switch MUST
// default to disabled.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.5.
layers.NewDHCPOption(layers.DHCPOptSourceRouting, []byte{0x0}),

// Do not set the Policy Filter Option since it only makes sense when
// the non-local source routing is enabled.

// The minimum legal value is 576.
//
// See https://datatracker.ietf.org/doc/html/rfc2132#section-4.4.
layers.NewDHCPOption(layers.DHCPOptDatagramMTU, []byte{0x2, 0x40}),

// Set the current recommended default time to live for the Internet
// Protocol which is 64.
//
// See https://www.iana.org/assignments/ip-parameters/ip-parameters.xhtml#ip-parameters-2.
layers.NewDHCPOption(layers.DHCPOptDefaultTTL, []byte{0x40}),

// For example, after the PTMU estimate is decreased, the timeout should
// be set to 10 minutes; once this timer expires and a larger MTU is
// attempted, the timeout can be set to a much smaller value.
//
// See https://datatracker.ietf.org/doc/html/rfc1191#section-6.6.
layers.NewDHCPOption(layers.DHCPOptPathMTUAgingTimeout, []byte{0x0, 0x0, 0x2, 0x58}),

// There is a table describing the MTU values representing all major
// data-link technologies in use in the Internet so that each set of
// similar MTUs is associated with a plateau value equal to the lowest
// MTU in the group.
//
// See https://datatracker.ietf.org/doc/html/rfc1191#section-7.
layers.NewDHCPOption(layers.DHCPOptPathPlateuTableOption, []byte{
0x0, 0x44,
0x1, 0x28,
0x1, 0xFC,
0x3, 0xEE,
0x5, 0xD4,
0x7, 0xD2,
0x11, 0x0,
0x1F, 0xE6,
0x45, 0xFA,
}),

// IP-Layer Per Interface

// Don't set the Interface MTU because client may choose the value on
// their own since it's listed in the [Host Requirements RFC]. It also
// seems the values listed there sometimes appear obsolete, see
// https://github.com/AdguardTeam/AdGuardHome/issues/5281.
//
// [Host Requirements RFC]: https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.3.

// Set the All Subnets Are Local Option to false since commonly the
// connected hosts aren't expected to be multihomed.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.3.
layers.NewDHCPOption(layers.DHCPOptAllSubsLocal, []byte{0x0}),

// Set the Perform Mask Discovery Option to false to provide the subnet
// mask by options only.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.2.9.
layers.NewDHCPOption(layers.DHCPOptMaskDiscovery, []byte{0x0}),

// A system MUST NOT send an Address Mask Reply unless it is an
// authoritative agent for address masks. An authoritative agent may be
// a host or a gateway, but it MUST be explicitly configured as a
// address mask agent.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.2.9.
layers.NewDHCPOption(layers.DHCPOptMaskSupplier, []byte{0x0}),

// Set the Perform Router Discovery Option to true as per Router
// Discovery Document.
//
// See https://datatracker.ietf.org/doc/html/rfc1256#section-5.1.
layers.NewDHCPOption(layers.DHCPOptRouterDiscovery, []byte{0x1}),

// The all-routers address is preferred wherever possible.
//
// See https://datatracker.ietf.org/doc/html/rfc1256#section-5.1.
layers.NewDHCPOption(layers.DHCPOptSolicitAddr, netutil.IPv4allrouter()),

// Don't set the Static Routes Option since it should be set up by
// system administrator.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.1.2.

// A datagram with the destination address of limited broadcast will be
// received by every host on the connected physical network but will not
// be forwarded outside that network.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.1.3.
layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, netutil.IPv4bcast()),

// Link-Layer Per Interface

// If the system does not dynamically negotiate use of the trailer
// protocol on a per-destination basis, the default configuration MUST
// disable the protocol.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-2.3.1.
layers.NewDHCPOption(layers.DHCPOptARPTrailers, []byte{0x0}),

// For proxy ARP situations, the timeout needs to be on the order of a
// minute.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-2.3.2.1.
layers.NewDHCPOption(layers.DHCPOptARPTimeout, []byte{0x0, 0x0, 0x0, 0x3C}),

// An Internet host that implements sending both the RFC-894 and the
// RFC-1042 encapsulations MUST provide a configuration switch to select
// which is sent, and this switch MUST default to RFC-894.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-2.3.3.
layers.NewDHCPOption(layers.DHCPOptEthernetEncap, []byte{0x0}),

// TCP Per Host

// A fixed value must be at least big enough for the Internet diameter,
// i.e., the longest possible path. A reasonable value is about twice
// the diameter, to allow for continued Internet growth.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.1.7.
layers.NewDHCPOption(layers.DHCPOptTCPTTL, []byte{0x0, 0x0, 0x0, 0x3C}),

// The interval MUST be configurable and MUST default to no less than
// two hours.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-4.2.3.6.
layers.NewDHCPOption(layers.DHCPOptTCPKeepAliveInt, []byte{0x0, 0x0, 0x1C, 0x20}),

// Unfortunately, some misbehaved TCP implementations fail to respond to
// a probe segment unless it contains data.
//
// See https://datatracker.ietf.org/doc/html/rfc1122#section-4.2.3.6.
layers.NewDHCPOption(layers.DHCPOptTCPKeepAliveGarbage, []byte{0x1}),
}
slices.SortFunc(implicit, compareV4OptionCodes)

// Set values for explicitly configured options.
for _, exp := range conf.Options {
i, found := slices.BinarySearchFunc(implicit, exp, compareV4OptionCodes)
if found {
implicit = slices.Delete(implicit, i, i+1)
}

i, found = slices.BinarySearchFunc(explicit, exp, compareV4OptionCodes)
if exp.Length > 0 {
explicit = slices.Insert(explicit, i, exp)
} else if found {
explicit = slices.Delete(explicit, i, i+1)
}
}

log.Debug("dhcpsvc: v4: implicit options: %s", implicit)
log.Debug("dhcpsvc: v4: explicit options: %s", explicit)

return implicit, explicit
}

// compareV4OptionCodes compares option codes of a and b.
func compareV4OptionCodes(a, b layers.DHCPOption) (res int) {
return int(a.Type) - int(b.Type)
}
88 changes: 88 additions & 0 deletions internal/dhcpsvc/v4_internal_test.go
View file
@@ -0,0 +1,88 @@
package dhcpsvc

import (
"net/netip"
"testing"

"github.com/google/gopacket/layers"
"github.com/stretchr/testify/assert"
)

func TestIPv4Config_Options(t *testing.T) {
oneIP, otherIP := netip.MustParseAddr("1.2.3.4"), netip.MustParseAddr("5.6.7.8")
subnetMask := netip.MustParseAddr("255.255.0.0")

opt1 := layers.NewDHCPOption(layers.DHCPOptSubnetMask, subnetMask.AsSlice())
opt6 := layers.NewDHCPOption(layers.DHCPOptDNS, append(oneIP.AsSlice(), otherIP.AsSlice()...))
opt28 := layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, oneIP.AsSlice())
opt121 := layers.NewDHCPOption(layers.DHCPOptClasslessStaticRoute, []byte("cba"))

testCases := []struct {
name string
conf *IPv4Config
wantExplicit layers.DHCPOptions
}{{
name: "all_default",
conf: &IPv4Config{
Options: nil,
},
wantExplicit: nil,
}, {
name: "configured_ip",
conf: &IPv4Config{
Options: layers.DHCPOptions{opt28},
},
wantExplicit: layers.DHCPOptions{opt28},
}, {
name: "configured_ips",
conf: &IPv4Config{
Options: layers.DHCPOptions{opt6},
},
wantExplicit: layers.DHCPOptions{opt6},
}, {
name: "configured_del",
conf: &IPv4Config{
Options: layers.DHCPOptions{
layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, nil),
},
},
wantExplicit: nil,
}, {
name: "rewritten_del",
conf: &IPv4Config{
Options: layers.DHCPOptions{
layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, nil),
opt28,
},
},
wantExplicit: layers.DHCPOptions{opt28},
}, {
name: "configured_and_del",
conf: &IPv4Config{
Options: layers.DHCPOptions{
layers.NewDHCPOption(layers.DHCPOptClasslessStaticRoute, []byte("a")),
layers.NewDHCPOption(layers.DHCPOptClasslessStaticRoute, nil),
opt121,
},
},
wantExplicit: layers.DHCPOptions{opt121},
}, {
name: "replace_config_value",
conf: &IPv4Config{
SubnetMask: netip.MustParseAddr("255.255.255.0"),
Options: layers.DHCPOptions{opt1},
},
wantExplicit: layers.DHCPOptions{opt1},
}}

for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
imp, exp := tc.conf.options()
assert.Equal(t, tc.wantExplicit, exp)

for c := range exp {
assert.NotContains(t, imp, c)
}
})
}
}

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