// SPDX-License-Identifier: GPL-3.0-or-later

// Package rootcheck ports Sentinel's user-space anti-rootkit cross-view
// checks. It cannot prove a kernel free of a rootkit: a sufficiently capable
// implant can lie consistently to every local view. It does catch common
// hiding faults by comparing independently collected kernel, procfs, sysfs,
// socket-tool, and interface views.
package rootcheck

import (
	"sort"
	"strconv"
	"strings"

	"codeberg.org/anassaeneroi/enodia-sentinal/go-agent/internal/model"
)

const (
	SIDHiddenProcess        = 100022
	SIDHiddenModule         = 100023
	SIDHiddenPort           = 100024
	SIDPromiscuous          = 100025
	SIDKnownRootkitModule   = 100028
	SIDTaintedModule        = 100029
	SIDKernelTainted        = 100030
	SIDHiddenUDPPort        = 100031
	SIDHiddenRawSocket      = 100034
	SIDRawICMPSocket        = 100035
	SIDHiddenProtocolSocket = 100037
	SIDPSHiddenProcess      = 100038
)

var knownModules = map[string]bool{
	"adore": true, "adore_ng": true, "azazel": true, "diamorphine": true,
	"ipsecs_kbeast": true, "kbeast": true, "knark": true, "reptile": true,
	"suterusu": true, "syslogk": true,
}

var taintFlags = map[int]string{
	0: "proprietary-module", 1: "forced-module-load", 2: "unsafe-smp",
	3: "forced-module-unload", 4: "machine-check", 5: "bad-page",
	6: "user-tainted", 7: "kernel-died-recently", 8: "acpi-override",
	9: "kernel-warning", 10: "staging-driver", 11: "firmware-workaround",
	12: "out-of-tree-module", 13: "unsigned-module", 14: "soft-lockup",
	15: "live-patched", 16: "auxiliary-taint", 17: "randstruct-plugin",
}

var highRiskTaintBits = map[int]bool{1: true, 3: true, 7: true, 12: true, 13: true}
var rawProtocolNames = map[string]int{"icmp": 1, "ipv6-icmp": 58, "icmp6": 58, "sctp": 132}

// Views contains independently collected host observations. The two PID
// callbacks preserve Python's race checks: a hidden-process candidate must
// still be alive through the kernel while remaining absent from procfs; a
// ps-only candidate must still be present in procfs.
type Views struct {
	VisiblePIDs       map[int]bool
	AlivePIDs         map[int]bool
	PSPIDs            map[int]bool
	PSAvailable       bool
	PIDAlive          func(int) bool
	ProcPIDExists     func(int) bool
	ProcModules       map[string]bool
	SysLiveModules    map[string]bool
	ModuleTaints      map[string]string
	KernelTaint       int
	ProcTCPPorts      map[int]bool
	SSTCPPorts        map[int]bool
	ProcUDPPorts      map[int]bool
	SSUDPPorts        map[int]bool
	ProcRawProtocols  map[int]bool
	SSRawProtocols    map[int]bool
	ProcProtocolKinds map[string]bool
	SSProtocolKinds   map[string]bool
	PromiscuousIfaces []string
}

// Options supplies explicit operator policy. The PID cap is enforced by the
// collector; Check is deliberately pure so parity tests do not touch a host.
type Options struct {
	AllowedModules map[string]bool
}

// Check turns a captured set of cross-views into Python-compatible alerts.
func Check(views Views, options Options) []model.Alert {
	alerts := make([]model.Alert, 0)
	confirmed := make([]int, 0)
	for _, pid := range sortedIntDifference(views.AlivePIDs, views.VisiblePIDs) {
		alive := views.PIDAlive == nil || views.PIDAlive(pid)
		hidden := views.ProcPIDExists == nil || !views.ProcPIDExists(pid)
		if alive && hidden {
			confirmed = append(confirmed, pid)
		}
	}
	if len(confirmed) > 0 {
		shown := confirmed
		if len(shown) > 20 {
			shown = shown[:20]
		}
		alerts = append(alerts, model.Alert{SID: SIDHiddenProcess, Severity: "CRITICAL",
			Signature: "rootkit_hidden_process", Classtype: "rootkit-hidden-process",
			Key:    "rk:hidproc:" + itoa(shown[0]),
			Detail: "process(es) alive but hidden from /proc: " + joinInts(shown), PIDs: shown})
	}

	if views.PSAvailable {
		missing := make([]int, 0)
		for _, pid := range sortedIntDifference(views.VisiblePIDs, views.PSPIDs) {
			if views.ProcPIDExists == nil || views.ProcPIDExists(pid) {
				missing = append(missing, pid)
			}
		}
		if len(missing) > 0 {
			shown := missing
			if len(shown) > 20 {
				shown = shown[:20]
			}
			alerts = append(alerts, model.Alert{SID: SIDPSHiddenProcess, Severity: "HIGH",
				Signature: "rootkit_ps_hidden_process", Classtype: "rootkit-hidden-process",
				Key:    "rk:pshidproc:" + itoa(shown[0]),
				Detail: "process(es) visible in /proc but missing from ps output (process tool may be hooked): " + joinInts(shown), PIDs: shown})
		}
	}

	for _, module := range sortedStringDifference(views.SysLiveModules, views.ProcModules) {
		alerts = append(alerts, alert(SIDHiddenModule, "CRITICAL", "rootkit_hidden_module", "rootkit-hidden-module", "rk:hidmod:"+module,
			"kernel module live in /sys/module but hidden from /proc/modules: "+module))
	}
	allModules := unionStrings(views.ProcModules, views.SysLiveModules)
	known := map[string]bool{}
	for module := range allModules {
		if knownModules[normalizeModule(module)] {
			known[module] = true
			alerts = append(alerts, alert(SIDKnownRootkitModule, "CRITICAL", "rootkit_known_module", "rootkit-known-module", "rk:knownmod:"+module,
				"known LKM rootkit module name loaded or visible: "+module))
		}
	}
	for _, module := range sortedKeysString(views.ModuleTaints) {
		if moduleAllowed(options.AllowedModules, module) || known[module] {
			continue
		}
		taint := views.ModuleTaints[module]
		alerts = append(alerts, alert(SIDTaintedModule, "HIGH", "rootkit_tainted_module", "rootkit-tainted-module", "rk:taintmod:"+module,
			"kernel module has taint marker '"+taint+"' (out-of-tree/proprietary/unsigned module): "+module))
	}
	if views.KernelTaint != 0 {
		severity := "MEDIUM"
		for bit := range highRiskTaintBits {
			if views.KernelTaint&(1<<bit) != 0 {
				severity = "HIGH"
				break
			}
		}
		flags := decodeTaint(views.KernelTaint)
		label := strings.Join(flags, ", ")
		if label == "" {
			label = "unknown"
		}
		alerts = append(alerts, alert(SIDKernelTainted, severity, "kernel_tainted", "kernel-integrity", "rk:ktaint:"+itoa(views.KernelTaint),
			"kernel taint value "+itoa(views.KernelTaint)+" ("+label+") — may indicate unsigned/out-of-tree modules, forced loads, or kernel faults"))
	}

	alerts = appendPortAlert(alerts, sortedIntDifference(views.ProcTCPPorts, views.SSTCPPorts), SIDHiddenPort, "rootkit_hidden_port", "rk:hidport:",
		"listening port(s) in /proc/net/tcp not reported by ss (tool may be hooked): ", "rootkit-hidden-port")
	alerts = appendPortAlert(alerts, sortedIntDifference(views.ProcUDPPorts, views.SSUDPPorts), SIDHiddenUDPPort, "rootkit_hidden_udp_port", "rk:hidudp:",
		"UDP port(s) in /proc/net/udp not reported by ss (tool may be hooked): ", "rootkit-hidden-port")
	raw := sortedIntDifference(views.ProcRawProtocols, views.SSRawProtocols)
	alerts = appendPortAlert(alerts, raw, SIDHiddenRawSocket, "rootkit_hidden_raw_socket", "rk:hidraw:",
		"raw socket protocol(s) in /proc/net/raw not reported by ss (tool may be hooked): ", "rootkit-hidden-socket")
	icmp := make([]int, 0)
	for _, protocol := range sortedKeys(views.ProcRawProtocols) {
		if protocol == 1 || protocol == 58 {
			icmp = append(icmp, protocol)
		}
	}
	if len(icmp) > 0 {
		alerts = append(alerts, alert(SIDRawICMPSocket, "HIGH", "raw_icmp_socket", "raw-socket-backdoor", "rk:rawicmp:"+itoa(icmp[0]),
			"persistent raw ICMP socket protocol(s) visible in /proc/net/raw: "+joinInts(icmp)+" — validate authorized ping/monitoring tools or ICMP knockers"))
	}
	protocols := sortedStringDifference(views.ProcProtocolKinds, views.SSProtocolKinds)
	if len(protocols) > 0 {
		alerts = append(alerts, alert(SIDHiddenProtocolSocket, "HIGH", "rootkit_hidden_protocol_socket", "rootkit-hidden-socket", "rk:hidproto:"+protocols[0],
			"special protocol socket family present in /proc/net but absent from ss output (tool may be hooked): "+strings.Join(protocols, ", ")))
	}
	for _, iface := range sortedStrings(views.PromiscuousIfaces) {
		alerts = append(alerts, alert(SIDPromiscuous, "MEDIUM", "promiscuous_interface", "network-sniffer", "rk:promisc:"+iface,
			"interface in promiscuous mode (possible sniffer): "+iface))
	}
	return alerts
}

func appendPortAlert(alerts []model.Alert, values []int, sid int, signature, keyPrefix, detailPrefix, class string) []model.Alert {
	if len(values) == 0 {
		return alerts
	}
	return append(alerts, alert(sid, "HIGH", signature, class, keyPrefix+itoa(values[0]), detailPrefix+joinInts(values)))
}

func alert(sid int, severity, signature, class, key, detail string) model.Alert {
	return model.Alert{SID: sid, Severity: severity, Signature: signature, Classtype: class, Key: key, Detail: detail, PIDs: []int{}}
}

func normalizeModule(value string) string {
	return strings.ReplaceAll(strings.ToLower(value), "-", "_")
}

func moduleAllowed(allowed map[string]bool, module string) bool {
	for name := range allowed {
		if normalizeModule(name) == normalizeModule(module) {
			return true
		}
	}
	return false
}
func itoa(value int) string { return strconv.Itoa(value) }

func sortedIntDifference(left, right map[int]bool) []int {
	values := make([]int, 0)
	for value := range left {
		if !right[value] {
			values = append(values, value)
		}
	}
	sort.Ints(values)
	return values
}
func sortedStringDifference(left, right map[string]bool) []string {
	values := make([]string, 0)
	for value := range left {
		if !right[value] {
			values = append(values, value)
		}
	}
	sort.Strings(values)
	return values
}
func sortedKeys[V any](source map[int]V) []int {
	values := make([]int, 0, len(source))
	for value := range source {
		values = append(values, value)
	}
	sort.Ints(values)
	return values
}
func sortedStrings(values []string) []string {
	result := append([]string(nil), values...)
	sort.Strings(result)
	return result
}
func sortedKeysString[V any](source map[string]V) []string {
	values := make([]string, 0, len(source))
	for value := range source {
		values = append(values, value)
	}
	sort.Strings(values)
	return values
}
func unionStrings(left, right map[string]bool) map[string]bool {
	result := map[string]bool{}
	for value := range left {
		result[value] = true
	}
	for value := range right {
		result[value] = true
	}
	return result
}
func decodeTaint(value int) []string {
	keys := make([]int, 0, len(taintFlags))
	for bit := range taintFlags {
		keys = append(keys, bit)
	}
	sort.Ints(keys)
	values := make([]string, 0)
	for _, bit := range keys {
		if value&(1<<bit) != 0 {
			values = append(values, taintFlags[bit])
		}
	}
	return values
}
func joinInts(values []int) string {
	rendered := make([]string, len(values))
	for i, value := range values {
		rendered[i] = itoa(value)
	}
	return strings.Join(rendered, ", ")
}