From deb85fe10d3e14324731c23c05b3ea5a51255861 Mon Sep 17 00:00:00 2001
From: maride <git@maride.cc>
Date: Thu, 26 Oct 2023 13:40:55 +0200
Subject: [PATCH] Init

---
 README.md |  29 ++++++++++++
 go.mod    |   3 ++
 main.go   | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 162 insertions(+)
 create mode 100644 README.md
 create mode 100644 go.mod
 create mode 100644 main.go

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..fd3fa88
--- /dev/null
+++ b/README.md
@@ -0,0 +1,29 @@
+# Ghost
+
+*Your friendly helper with /etc/hosts, written in Go!*
+
+## Features
+
+- Extending existing lines
+- Deduplication
+- Format check
+- `SUID` safe!
+
+## Usage
+
+To add two domain names, `domain1.foo` and `domain2.bar`, for the IP addres `10.0.0.1`:
+
+`./ghost 10.0.0.1 domain1.foo domain2.bar`
+
+The added line will look like this:
+
+```
+10.0.0.1        domain1.foo domain2.bar # Added by ghost on 26-10-2023
+```
+
+## Notes
+
+The tool is safe to use with the [SUID bit](https://www.redhat.com/sysadmin/suid-sgid-sticky-bit), which is very handy for not entering your password when adding hostnames to your `/etc/hosts` file every time.
+
+While this is very handy for CTFs or platforms like Hack The Box, this is also a big security issue, e.g. if you are on a multi-user machine. **Use with caution!**
+
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..b991399
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module git.maride.cc/maride/ghost
+
+go 1.21.3
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..c05ce51
--- /dev/null
+++ b/main.go
@@ -0,0 +1,130 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"regexp"
+	"strings"
+	"time"
+)
+
+func main() {
+	targetIP, domains := parseArgs()
+	motd()
+	process(targetIP, domains)
+}
+
+func parseArgs() (net.IP, []string) {
+	// Check for arguments
+	if len(os.Args) < 3 {
+		usage()
+		os.Exit(1)
+	}
+
+	// Parse IP
+	rawIP := os.Args[1]
+	ip := net.ParseIP(rawIP)
+	if ip == nil {
+		fmt.Fprintf(os.Stderr, "Not an IP address: %s\n", rawIP)
+		usage()
+		os.Exit(1)
+	}
+
+	// Check for formatting of domain names
+	domainExpr, _ := regexp.Compile("^([a-zA-Z0-9]+[a-zA-Z0-9\\-]*[a-zA-Z0-9]+.{0,1})+$")
+	for _, a := range os.Args[2:] {
+		if !domainExpr.MatchString(a) {
+			fmt.Fprintf(os.Stderr, "Doesn't look like a valid domain: %s\n", a)
+			usage()
+			os.Exit(1)
+		}
+	}
+
+	// All parsed and correct
+	return ip, os.Args[2:]
+}
+
+// process goes over the /etc/hosts and tries to best-fit the domain names for the IP
+func process(ip net.IP, domains []string) {
+	// Read file
+	bytesEtcHosts, readErr := os.ReadFile("/etc/hosts")
+	if readErr != nil {
+		fmt.Fprintf(os.Stderr, "Failed to read /etc/hosts: %s\n", readErr.Error())
+		os.Exit(1)
+	}
+	etcHosts := string(bytesEtcHosts)
+
+	// Iterate over lines, find the first match for the IP
+	lines := strings.Split(etcHosts, "\n")
+	ipString := ip.String()
+	found := false
+	for lPos, l := range lines {
+		if strings.HasPrefix(l, ipString) {
+			// Matching line, append our domains.
+
+			// Avoid duplicates
+			fields := strings.Fields(l)
+			newDomainsArray := []string{}
+			ignore := false
+			for _, d := range domains {
+				for _, f := range fields {
+					if d == f {
+						// this domain name is already in the hosts file, skip
+						ignore = true
+						break
+					}
+				}
+				if !ignore {
+					newDomainsArray = append(newDomainsArray, d)
+				}
+			}
+			newDomains := strings.Join(newDomainsArray, " ")
+
+			// Preserve comments and construct the line again
+			hostLine, comment, hasComment := strings.Cut(l, "#")
+			if hasComment {
+				lines[lPos] = fmt.Sprintf("%s %s # %s", hostLine, newDomains, comment)
+			} else {
+				lines[lPos] = fmt.Sprintf("%s %s", hostLine, newDomains)
+			}
+			found = true
+		}
+	}
+
+	// If a fitting line was not found in the previous for loop, append a new line
+	if !found {
+		newDomains := strings.Join(domains, " ")
+		date := time.Now().Format("02-01-2006")
+		newLine := fmt.Sprintf("%s\t%s # Added by ghost on %s", ipString, newDomains, date)
+		lines = append(lines, newLine)
+	}
+
+	// Write out again
+	newHosts := strings.Join(lines, "\n")
+	writeErr := os.WriteFile("/etc/hosts", []byte(newHosts), 0o644)
+	if writeErr != nil {
+		fmt.Fprintf(os.Stderr, "Failed to write /etc/hosts: %s\n", writeErr.Error())
+		os.Exit(1)
+	}
+}
+
+// usage prints the usage
+func usage() {
+	fmt.Fprintf(os.Stderr, "Usage: ghost 10.0.1.1 server1.gh <foo.server2.gh> <www.server2.gh> ...\n")
+}
+
+// motd prints the banner at the start, fully easter-egg free
+func motd() {
+	fmt.Println("+-------------------------+")
+	if(time.Now().Month() == time.October) {
+		// I mean, it's called 'ghost' after all...
+		fmt.Println("👻 🕷️ 🎃 G H O S T 🎃 🕷️ 👻")
+		fmt.Println(" your spooooky helper with ")
+	} else {
+		fmt.Println("         G H O S T         ")
+		fmt.Println(" your friendly helper with ")
+	}
+	fmt.Println(" /etc/hosts, written in Go!")
+	fmt.Println("+-------------------------+")
+}