From 7584817e7b1084ca9010fa4f7a4036499da33943 Mon Sep 17 00:00:00 2001
From: Mahmoud Nada <mahmoudn@google.com>
Date: Mon, 6 May 2024 19:38:30 +0000
Subject: [PATCH] Use signed-by keyring approach for apt repos in Debian 12+
 and Ubuntu 24+

---
 policies/apt.go      | 64 ++++++++++++++++++++++++++++++++++++++------
 policies/apt_test.go | 28 +++++++++++++++++++
 2 files changed, 84 insertions(+), 8 deletions(-)

diff --git a/policies/apt.go b/policies/apt.go
index d32639813..74d619f37 100644
--- a/policies/apt.go
+++ b/policies/apt.go
@@ -22,9 +22,11 @@ import (
 	"io"
 	"net/http"
 	"sort"
+	"strconv"
 	"strings"
 
 	"github.com/GoogleCloudPlatform/osconfig/clog"
+	"github.com/GoogleCloudPlatform/osconfig/osinfo"
 	"github.com/GoogleCloudPlatform/osconfig/packages"
 	"golang.org/x/crypto/openpgp"
 	"golang.org/x/crypto/openpgp/armor"
@@ -83,6 +85,52 @@ func containsEntity(es []*openpgp.Entity, e *openpgp.Entity) bool {
 	return false
 }
 
+func readInstanceOsInfo() (string, float64, error) {
+	oi, err := osinfo.Get()
+	if err != nil {
+		return "", 0, fmt.Errorf("error getting osinfo: %v", err)
+	}
+
+	osVersion, err := strconv.ParseFloat(oi.Version, 64)
+	if err != nil {
+		osVersion = 0
+	}
+
+	return oi.ShortName, osVersion, nil
+}
+
+func shouldUseSignedBy() bool {
+	osShortName, osVersion, err := readInstanceOsInfo()
+	if err != nil {
+		return false // Default to not using signed-by approach
+	}
+
+	if (osShortName == "debian" && osVersion >= 12) || (osShortName == "ubuntu" && osVersion >= 24) {
+		return true
+	}
+	return false
+}
+
+func getAptRepoLine(repo *agentendpointpb.AptRepository, useSignedBy bool) string {
+	archiveType, ok := debArchiveTypeMap[repo.ArchiveType]
+	if !ok {
+		archiveType = "deb"
+	}
+
+	line := fmt.Sprintf("\n%s", archiveType)
+
+	if useSignedBy {
+		line = fmt.Sprintf("%s [signed-by=%s]", line, aptGPGFile)
+	}
+
+	line = fmt.Sprintf("%s %s %s", line, repo.Uri, repo.Distribution)
+	for _, c := range repo.Components {
+		line = fmt.Sprintf("%s %s", line, c)
+	}
+
+	return line
+}
+
 func aptRepositories(ctx context.Context, repos []*agentendpointpb.AptRepository, repoFile string) error {
 	var es []*openpgp.Entity
 	var keys []string
@@ -124,18 +172,18 @@ func aptRepositories(ctx context.Context, repos []*agentendpointpb.AptRepository
 		# Repo file managed by Google OSConfig agent
 		deb http://repo1-url/ repo1 main
 		deb http://repo1-url/ repo2 main contrib non-free
+
+		# For now, 'signed-by' keyring approach will be used for Debian 12+ and Ubuntu 24+ only.
+		  To avoid conflicting repos for old stable OSes versions
+		  e.g. deb [signed-by=/etc/apt/trusted.gpg.d/osconfig_agent_managed.gpg] http://repo1-url/ repo1 main
+		  NOTE: suggested by ofca@
 	*/
 	var buf bytes.Buffer
 	buf.WriteString("# Repo file managed by Google OSConfig agent\n")
+
+	shouldUseSignedByBool := shouldUseSignedBy()
 	for _, repo := range repos {
-		archiveType, ok := debArchiveTypeMap[repo.ArchiveType]
-		if !ok {
-			archiveType = "deb"
-		}
-		line := fmt.Sprintf("\n%s %s %s", archiveType, repo.Uri, repo.Distribution)
-		for _, c := range repo.Components {
-			line = fmt.Sprintf("%s %s", line, c)
-		}
+		line := getAptRepoLine(repo, shouldUseSignedByBool)
 		buf.WriteString(line + "\n")
 	}
 
diff --git a/policies/apt_test.go b/policies/apt_test.go
index fc9f65129..6a8c2d311 100644
--- a/policies/apt_test.go
+++ b/policies/apt_test.go
@@ -108,3 +108,31 @@ func TestGetAptGPGKey(t *testing.T) {
 		t.Errorf("Expected to find Artifact Registry key in Google Cloud Public GPG key, but its missed.")
 	}
 }
+
+func TestUseSignedBy(t *testing.T) {
+	tests := []struct {
+		desc string
+		repo *agentendpointpb.AptRepository
+		want string
+	}{
+		{
+			"1 repo",
+			&agentendpointpb.AptRepository{Uri: "http://repo1-url/", Distribution: "distribution", Components: []string{"component1"}},
+			"\ndeb [signed-by=/etc/apt/trusted.gpg.d/osconfig_agent_managed.gpg] http://repo1-url/ distribution component1",
+		},
+		{
+			"2 components",
+			&agentendpointpb.AptRepository{Uri: "http://repo2-url/", Distribution: "distribution", Components: []string{"component1", "component2"}, ArchiveType: agentendpointpb.AptRepository_DEB},
+			"\ndeb [signed-by=/etc/apt/trusted.gpg.d/osconfig_agent_managed.gpg] http://repo2-url/ distribution component1 component2",
+		},
+	}
+
+	useSignedBy := true
+	for _, tt := range tests {
+		aptRepoLine := getAptRepoLine(tt.repo, useSignedBy)
+
+		if aptRepoLine != tt.want {
+			t.Errorf("%s: got:\n%q\nwant:\n%q", tt.desc, aptRepoLine, tt.want)
+		}
+	}
+}