app: generate and replace passwd and group files

This ensures libc functions get correct user information.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/app/share.system.go

@@ -0,0 +1,43 @@
+package app
+
+import (
+	"os"
+	"path"
+)
+
+const (
+	shell = "SHELL"
+)
+
+// shareSystem queues various system-related actions
+func (seal *appSeal) shareSystem() {
+	// look up shell
+	sh := "/bin/sh"
+	if s, ok := os.LookupEnv(shell); ok {
+		seal.sys.setEnv(shell, s)
+		sh = s
+	}
+
+	// generate /etc/passwd
+	passwdPath := path.Join(seal.share, "passwd")
+	username := "chronos"
+	if seal.sys.Username != "" {
+		username = seal.sys.Username
+		seal.sys.setEnv("USER", seal.sys.Username)
+	}
+	homeDir := "/var/empty"
+	if seal.sys.HomeDir != "" {
+		homeDir = seal.sys.HomeDir
+		seal.sys.setEnv("HOME", seal.sys.HomeDir)
+	}
+	passwd := username + ":x:65534:65534:Fortify:" + homeDir + ":" + sh + "\n"
+	seal.sys.writeFile(passwdPath, []byte(passwd))
+
+	// write /etc/group
+	groupPath := path.Join(seal.share, "group")
+	seal.sys.writeFile(groupPath, []byte("fortify:x:65534:\n"))
+
+	// bind /etc/passwd and /etc/group
+	seal.sys.bind(passwdPath, "/etc/passwd", true)
+	seal.sys.bind(groupPath, "/etc/group", true)
+}