feat: detect Debian version from /etc/debian_version (#4569)

Signed-off-by: Keith Zantow <kzantow@gmail.com>

syft/linux/identify_release.go

@@ -54,6 +54,12 @@ var identityFiles = []parseEntry{
 	// /////////////////////////////////////////////////////////////////////////////////////////////////////
 }
 
+// after a parser function returns a Release, it may have incomplete information; supplementers can be used to
+// fill in missing details based on other files present in the filesystem
+var supplementers = []func(file.Resolver, *Release){
+	supplementDebianVersion,
+}
+
 // IdentifyRelease parses distro-specific files to discover and raise linux distribution release details.
 func IdentifyRelease(resolver file.Resolver) *Release {
 	logger := log.Nested("operation", "identify-release")
@@ -67,6 +73,9 @@ func IdentifyRelease(resolver file.Resolver) *Release {
 		for _, location := range locations {
 			release := tryParseReleaseInfo(resolver, location, logger, entry)
 			if release != nil {
+				for _, supplementer := range supplementers {
+					supplementer(resolver, release)
+				}
 				return release
 			}
 		}

syft/linux/identify_release_test.go

@@ -74,7 +74,7 @@ func TestIdentifyRelease(t *testing.T) {
 			},
 		},
 		{
-			fixture: "test-fixtures/os/debian",
+			fixture: "test-fixtures/os/debian/from-os-release",
 			release: &Release{
 				PrettyName:   "Debian GNU/Linux 8 (jessie)",
 				Name:         "Debian GNU/Linux",
@@ -87,6 +87,20 @@ func TestIdentifyRelease(t *testing.T) {
 				BugReportURL: "https://bugs.debian.org/",
 			},
 		},
+		{
+			fixture: "test-fixtures/os/debian/from-debian_version",
+			release: &Release{
+				PrettyName:   "Distroless",
+				Name:         "Debian GNU/Linux",
+				ID:           "debian",
+				IDLike:       nil,
+				Version:      "10.8",
+				VersionID:    "10.8",
+				HomeURL:      "https://github.com/GoogleContainerTools/distroless",
+				SupportURL:   "https://github.com/GoogleContainerTools/distroless/blob/master/README.md",
+				BugReportURL: "https://github.com/GoogleContainerTools/distroless/issues/new",
+			},
+		},
 		{
 			fixture: "test-fixtures/os/fedora",
 			release: &Release{

syft/linux/supplement_release.go

@@ -0,0 +1,51 @@
+package linux
+
+import (
+	"io"
+	"regexp"
+	"strings"
+
+	"github.com/anchore/syft/internal"
+	"github.com/anchore/syft/internal/log"
+	"github.com/anchore/syft/syft/file"
+)
+
+func supplementDebianVersion(resolver file.Resolver, release *Release) {
+	// we're only looking for version information for debian when none is present in /etc/os-release
+	if release.Version != "" || release.VersionID != "" || !strings.EqualFold(release.ID, "debian") {
+		return
+	}
+	// if we have a debian release with no version, look for a debian_version
+	locations, err := resolver.FilesByGlob("/etc/debian_version")
+	if err != nil {
+		log.Debugf("error reading /etc/debian_version: %v", err)
+		return
+	}
+	for _, location := range locations {
+		version := readDebianVersionFile(resolver, location)
+		if version != "" {
+			release.Version = version
+			release.VersionID = version
+			return // keep the first result
+		}
+	}
+}
+
+func readDebianVersionFile(resolver file.Resolver, location file.Location) string {
+	rdr, err := resolver.FileContentsByLocation(location)
+	if err != nil {
+		log.Debugf("error getting contents for %s: %v", location.RealPath, err)
+		return ""
+	}
+	defer internal.CloseAndLogError(rdr, location.RealPath)
+	contents, err := io.ReadAll(rdr)
+	if err != nil {
+		log.Debugf("error reading %s: %v", location.RealPath, err)
+		return ""
+	}
+	version := strings.TrimSpace(string(contents))
+	if regexp.MustCompile(`^\d+(?:\.\d+)?$`).MatchString(version) {
+		return version
+	}
+	return ""
+}

syft/linux/test-fixtures/os/debian/from-debian_version/etc/debian_version

@@ -0,0 +1 @@
+10.8

syft/linux/test-fixtures/os/debian/from-debian_version/etc/os-release

@@ -0,0 +1,6 @@
+PRETTY_NAME="Distroless"
+NAME="Debian GNU/Linux"
+ID="debian"
+HOME_URL="https://github.com/GoogleContainerTools/distroless"
+SUPPORT_URL="https://github.com/GoogleContainerTools/distroless/blob/master/README.md"
+BUG_REPORT_URL="https://github.com/GoogleContainerTools/distroless/issues/new"