detect Ubuntu Pro/ESM extended support (#5028)

Mirrors the existing RHEL `ExtendedSupport` detector for Ubuntu so grype can
auto-enable its ESM distro channel on Pro/ESM-enabled scans.

`findUbuntuFeatures` sets `linux.Release.ExtendedSupport` when the scanned OS is
Ubuntu and any of these hold:

- an uncommented apt source (classic `.list` or DEB822 `.sources`, or the
  ubuntu-advantage auth entry) referencing `esm.ubuntu.com`
- an enabled `esm-infra`/`esm-apps` service in the ubuntu-advantage
  `status.json` cache
- an installed dpkg package whose version carries an `[~+]esm` pocket suffix
  (the usual in-image signal, since containers are rarely Pro-attached)

The package fallback reads `s.Artifacts.Packages` from the `DetectFeatures`
SBOM callback, which runs after package cataloging, so no new plumbing was
needed. Conservative by design: plain Ubuntu and disabled/commented ESM
evidence stay false.

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

internal/os/feature_detection_test.go

@@ -2,6 +2,11 @@ package os_test
 
 import (
 	"context"
+	"io"
+	stdos "os"
+	"path"
+	"path/filepath"
+	"slices"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -11,7 +16,9 @@ import (
 	"github.com/anchore/syft/internal/sbomsync"
 	"github.com/anchore/syft/internal/task"
 	"github.com/anchore/syft/syft"
+	"github.com/anchore/syft/syft/file"
 	"github.com/anchore/syft/syft/linux"
+	"github.com/anchore/syft/syft/pkg"
 	"github.com/anchore/syft/syft/sbom"
 	"github.com/anchore/syft/syft/source"
 )
@@ -99,3 +106,210 @@ func Test_EnvironmentTask(t *testing.T) {
 		})
 	}
 }
+
+func Test_findUbuntuFeatures(t *testing.T) {
+	tests := []struct {
+		name      string
+		dir       string
+		releaseID string
+		packages  []pkg.Package
+		expected  bool
+	}{
+		{
+			name:      "esm apt source present",
+			dir:       "testdata/ubuntu_esm_apt",
+			releaseID: "ubuntu",
+			expected:  true,
+		},
+		{
+			name:      "esm apt source in DEB822 .sources format",
+			dir:       "testdata/ubuntu_esm_deb822",
+			releaseID: "ubuntu",
+			expected:  true,
+		},
+		{
+			name:      "esm evidence in apt auth.conf.d",
+			dir:       "testdata/ubuntu_esm_authconf",
+			releaseID: "ubuntu",
+			expected:  true,
+		},
+		{
+			name:      "active esm service in ubuntu-advantage status",
+			dir:       "testdata/ubuntu_esm_status",
+			releaseID: "ubuntu",
+			expected:  true,
+		},
+		{
+			name:      "only esm-infra enabled (esm-apps disabled)",
+			dir:       "testdata/ubuntu_esm_infra_only",
+			releaseID: "ubuntu",
+			expected:  true,
+		},
+		{
+			name:      "malformed status.json does not panic or match",
+			dir:       "testdata/ubuntu_esm_malformed",
+			releaseID: "ubuntu",
+			expected:  false,
+		},
+		{
+			name:      "installed +esm package version",
+			dir:       "testdata/ubuntu_plain",
+			releaseID: "ubuntu",
+			packages: []pkg.Package{
+				{Name: "openssl", Version: "1.1.1f-1ubuntu2.19+esm1", Type: pkg.DebPkg},
+			},
+			expected: true,
+		},
+		{
+			name:      "installed ~esm package version",
+			dir:       "testdata/ubuntu_plain",
+			releaseID: "ubuntu",
+			packages: []pkg.Package{
+				{Name: "libcap2", Version: "1:2.32-1ubuntu0.1~esm1", Type: pkg.DebPkg},
+			},
+			expected: true,
+		},
+		{
+			name:      "plain ubuntu with no esm evidence",
+			dir:       "testdata/ubuntu_plain",
+			releaseID: "ubuntu",
+			packages: []pkg.Package{
+				{Name: "openssl", Version: "1.1.1f-1ubuntu2.19", Type: pkg.DebPkg},
+			},
+			expected: false,
+		},
+		{
+			name:      "commented esm source and disabled esm service",
+			dir:       "testdata/ubuntu_esm_disabled",
+			releaseID: "ubuntu",
+			expected:  false,
+		},
+		{
+			name:      "esm disabled but +esm package remains installed",
+			dir:       "testdata/ubuntu_esm_disabled",
+			releaseID: "ubuntu",
+			packages: []pkg.Package{
+				{Name: "openssl", Version: "1.1.1f-1ubuntu2.19+esm1", Type: pkg.DebPkg},
+			},
+			expected: true, // durable proof: ESM content is on disk even though the channel is now off
+		},
+		{
+			name:      "fips-only pro host is not plain esm",
+			dir:       "testdata/ubuntu_fips_only",
+			releaseID: "ubuntu",
+			expected:  false, // esm.ubuntu.com/fips must not be folded into the base esm channel
+		},
+		{
+			name:      "non-ubuntu is unaffected by esm evidence",
+			dir:       "testdata/ubuntu_esm_apt",
+			releaseID: "debian",
+			expected:  false,
+		},
+		{
+			name:      "non-ubuntu is unaffected by esm package version",
+			dir:       "testdata/ubuntu_plain",
+			releaseID: "debian",
+			packages: []pkg.Package{
+				{Name: "openssl", Version: "1.1.1f-1ubuntu2.19+esm1", Type: pkg.DebPkg},
+			},
+			expected: false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			resolver := fixtureResolverForDir(t, test.dir)
+
+			s := sbom.SBOM{}
+			s.Artifacts.LinuxDistribution = &linux.Release{ID: test.releaseID}
+			s.Artifacts.Packages = pkg.NewCollection(test.packages...)
+
+			err := os.DetectFeatures(context.Background(), resolver, sbomsync.NewBuilder(&s))
+			require.NoError(t, err)
+
+			require.Equal(t, test.expected, s.Artifacts.LinuxDistribution.ExtendedSupport)
+		})
+	}
+}
+
+// a read error in the apt-source signal must not suppress the ubuntu-advantage status signal; the three
+// signals are meant to be independent fallbacks.
+func Test_findUbuntuFeatures_signalErrorDoesNotSuppressOthers(t *testing.T) {
+	resolver := errOnGlobResolver{
+		fixtureResolver: fixtureResolverForDir(t, "testdata/ubuntu_esm_status").(fixtureResolver),
+		errOnGlob:       "/etc/apt/sources.list.d/*",
+	}
+
+	s := sbom.SBOM{}
+	s.Artifacts.LinuxDistribution = &linux.Release{ID: "ubuntu"}
+	s.Artifacts.Packages = pkg.NewCollection()
+
+	require.NoError(t, os.DetectFeatures(context.Background(), resolver, sbomsync.NewBuilder(&s)))
+
+	// the apt glob errors, but the status.json signal (esm-infra enabled) should still be consulted
+	require.True(t, s.Artifacts.LinuxDistribution.ExtendedSupport)
+}
+
+// errOnGlobResolver injects a failure for a specific glob to simulate an unreadable apt directory.
+type errOnGlobResolver struct {
+	fixtureResolver
+	errOnGlob string
+}
+
+func (r errOnGlobResolver) FilesByGlob(patterns ...string) ([]file.Location, error) {
+	if slices.Contains(patterns, r.errOnGlob) {
+		return nil, stdos.ErrPermission
+	}
+	return r.fixtureResolver.FilesByGlob(patterns...)
+}
+
+// fixtureResolver maps in-image logical paths to on-disk fixture files so DetectFeatures can be driven
+// without building a container image.
+type fixtureResolver struct {
+	file.Resolver // unused methods; nil is fine since only the three below are called
+	files         map[string]string
+}
+
+func (r fixtureResolver) FilesByGlob(patterns ...string) ([]file.Location, error) {
+	var out []file.Location
+	for logical := range r.files {
+		for _, p := range patterns {
+			if ok, _ := path.Match(p, logical); ok {
+				out = append(out, file.NewLocation(logical))
+				break
+			}
+		}
+	}
+	return out, nil
+}
+
+func (r fixtureResolver) FilesByPath(paths ...string) ([]file.Location, error) {
+	var out []file.Location
+	for _, p := range paths {
+		if _, ok := r.files[p]; ok {
+			out = append(out, file.NewLocation(p))
+		}
+	}
+	return out, nil
+}
+
+func (r fixtureResolver) FileContentsByLocation(l file.Location) (io.ReadCloser, error) {
+	return stdos.Open(r.files[l.RealPath])
+}
+
+func fixtureResolverForDir(t *testing.T, dir string) file.Resolver {
+	t.Helper()
+	files := map[string]string{}
+	require.NoError(t, filepath.WalkDir(dir, func(p string, d stdos.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		rel, err := filepath.Rel(dir, p)
+		if err != nil {
+			return err
+		}
+		files["/"+filepath.ToSlash(rel)] = p
+		return nil
+	}))
+	return fixtureResolver{files: files}
+}