From 6a6d30af1f15b0aa1b79174ecb08b59bd77dabb0 Mon Sep 17 00:00:00 2001
From: Ophestra Umiker <cat@ophivana.moe>
Date: Sun, 17 Nov 2024 02:03:18 +0900
Subject: [PATCH] cmd/fuserdb: systemd userdb drop-in entries generator

This provides user records via nss-systemd. Static drop-in entries are generated to reduce complexity and attack surface.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>
---
 cmd/fuserdb/main.go | 95 +++++++++++++++++++++++++++++++++++++++++++++
 package.nix         |  7 ++--
 2 files changed, 99 insertions(+), 3 deletions(-)
 create mode 100644 cmd/fuserdb/main.go

diff --git a/cmd/fuserdb/main.go b/cmd/fuserdb/main.go
new file mode 100644
index 0000000..9283d82
--- /dev/null
+++ b/cmd/fuserdb/main.go
@@ -0,0 +1,95 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"path"
+	"strconv"
+
+	"git.ophivana.moe/security/fortify/internal/fmsg"
+)
+
+func main() {
+	fmsg.SetPrefix("fuserdb")
+
+	const varEmpty = "/var/empty"
+
+	out := flag.String("o", "userdb", "output directory")
+	homeDir := flag.String("d", varEmpty, "parent of home directories")
+	shell := flag.String("s", "/sbin/nologin", "absolute path to subordinate user shell")
+	flag.Parse()
+
+	type user struct {
+		name string
+		fid  int
+	}
+
+	users := make([]user, len(flag.Args()))
+	for i, s := range flag.Args() {
+		f := bytes.SplitN([]byte(s), []byte{':'}, 2)
+		if len(f) != 2 {
+			fmsg.Fatalf("invalid entry at index %d", i)
+		}
+		users[i].name = string(f[0])
+		if fid, err := strconv.Atoi(string(f[1])); err != nil {
+			fmsg.Fatal(err.Error())
+		} else {
+			users[i].fid = fid
+		}
+	}
+
+	if err := os.MkdirAll(*out, 0755); err != nil && !errors.Is(err, os.ErrExist) {
+		fmsg.Fatalf("cannot create output: %v", err)
+	}
+
+	type payload struct {
+		UserName      string `json:"userName"`
+		Uid           int    `json:"uid"`
+		Gid           int    `json:"gid"`
+		RealName      string `json:"realName"`
+		HomeDirectory string `json:"homeDirectory"`
+		Shell         string `json:"shell"`
+	}
+
+	for _, u := range users {
+		fidString := strconv.Itoa(u.fid)
+		for aid := 0; aid < 9999; aid++ {
+			userName := fmt.Sprintf("u%d_a%d", u.fid, aid)
+			uid := 1000000 + u.fid*10000 + aid
+			us := strconv.Itoa(uid)
+			realName := fmt.Sprintf("Fortify subordinate user %d (%s)", aid, u.name)
+			var homeDirectory string
+			if *homeDir != varEmpty {
+				homeDirectory = path.Join(*homeDir, fidString, strconv.Itoa(aid))
+			} else {
+				homeDirectory = varEmpty
+			}
+
+			fileName := userName + ".user"
+			if f, err := os.OpenFile(path.Join(*out, fileName), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644); err != nil {
+				fmsg.Fatalf("cannot create %s: %v", userName, err)
+			} else if err = json.NewEncoder(f).Encode(&payload{
+				UserName:      userName,
+				Uid:           uid,
+				Gid:           uid,
+				RealName:      realName,
+				HomeDirectory: homeDirectory,
+				Shell:         *shell,
+			}); err != nil {
+				fmsg.Fatalf("cannot serialise %s: %v", userName, err)
+			} else if err = f.Close(); err != nil {
+				fmsg.Printf("cannot close %s: %v", userName, err)
+			}
+			if err := os.Symlink(fileName, path.Join(*out, us+".user")); err != nil {
+				fmsg.Fatalf("cannot link %s: %v", userName, err)
+			}
+		}
+	}
+
+	fmsg.Printf("created %d entries", len(users)*10000)
+	fmsg.Exit(0)
+}
diff --git a/package.nix b/package.nix
index ddc9d48..d510c64 100644
--- a/package.nix
+++ b/package.nix
@@ -31,12 +31,12 @@ buildGoModule rec {
         "-X"
         "main.Fmain=${placeholder "out"}/bin/.fortify-wrapped"
         "-X"
-        "main.Fshim=${placeholder "out"}/bin/fshim"
+        "main.Fshim=${placeholder "out"}/libexec/fshim"
       ]
       {
         Version = "v${version}";
         Fsu = "/run/wrappers/bin/fsu";
-        Finit = "${placeholder "out"}/bin/finit";
+        Finit = "${placeholder "out"}/libexec/finit";
       };
 
   buildInputs = [
@@ -54,6 +54,7 @@ buildGoModule rec {
       ]
     }
 
-    mv $out/bin/fsu $out/bin/.fsu
+    mkdir $out/libexec
+    (cd $out/bin && mv fsu fshim finit fuserdb ../libexec/)
   '';
 }