ldconfig: Create top-level conf file is none exists instead of a drop-in

Author: jfroy

internal/ldconfig/ldconfig.go

@@ -37,6 +37,15 @@ const (
 	// higher precedence than other libraries on the system, but lower than
 	// the 00-cuda-compat that is included in some containers.
 	ldsoconfdFilenamePattern = "00-nvcr-*.conf"
+	// defaultTopLevelLdsoconfFilePath is the standard location of the top-level ld.so.conf file.
+	// Most container images based on a distro will have this file, but distroless container images
+	// may not.
+	defaultTopLevelLdsoconfFilePath = "/etc/ld.so.conf"
+	// defaultLdsoconfdDir is the standard location for the ld.so.conf.d drop-in directory. Most
+	// container images based on a distro will have this directory included by the top-level
+	// ld.so.conf file, but some may not. And some container images may not have a top-level
+	// ld.so.conf file at all.
+	defaultLdsoconfdDir = "/etc/ld.so.conf.d"
 )
 
 type Ldconfig struct {
@@ -115,19 +124,18 @@ func (l *Ldconfig) UpdateLDCache() error {
 
 	// Explicitly specify using /etc/ld.so.conf since the host's ldconfig may
 	// be configured to use a different config file by default.
-	const topLevelLdsoconfFilePath = "/etc/ld.so.conf"
-	filteredDirectories, err := l.filterDirectories(topLevelLdsoconfFilePath, l.directories...)
+	filteredDirectories, err := l.filterDirectories(defaultTopLevelLdsoconfFilePath, l.directories...)
 	if err != nil {
 		return err
 	}
 
 	args := []string{
 		filepath.Base(ldconfigPath),
-		"-f", topLevelLdsoconfFilePath,
+		"-f", defaultTopLevelLdsoconfFilePath,
 		"-C", "/etc/ld.so.cache",
 	}
 
-	if err := createLdsoconfdFile(ldsoconfdFilenamePattern, filteredDirectories...); err != nil {
+	if err := createLdsoconfdFile(defaultTopLevelLdsoconfFilePath, defaultLdsoconfdDir, ldsoconfdFilenamePattern, filteredDirectories...); err != nil {
 		return fmt.Errorf("failed to update ld.so.conf.d: %w", err)
 	}
 
@@ -179,22 +187,30 @@ func (l *Ldconfig) filterDirectories(configFilePath string, directories ...strin
 	return filtered, nil
 }
 
-// createLdsoconfdFile creates a file at /etc/ld.so.conf.d/.
-// The file is created at /etc/ld.so.conf.d/{{ .pattern }} using `CreateTemp` and
-// contains the specified directories on each line.
-func createLdsoconfdFile(pattern string, dirs ...string) error {
+// createLdsoconfdFile creates a ldso conf file containing the specified directories on each line.
+//
+// The file is either created at `topLevelLdsoconfFilePath` if no file exists there, or as a
+// drop-in in `ldsoconfdDir` using `CreateTemp` and `pattern`. The function assumes that an
+// existing top-level ldso conf file includes `ldsoconfdDir`.
+func createLdsoconfdFile(topLevelLdsoconfFilePath, ldsoconfdDir, pattern string, dirs ...string) error {
 	if len(dirs) == 0 {
 		return nil
 	}
 
-	ldsoconfdDir := "/etc/ld.so.conf.d"
-	if err := os.MkdirAll(ldsoconfdDir, 0755); err != nil {
-		return fmt.Errorf("failed to create ld.so.conf.d: %w", err)
-	}
-
-	configFile, err := os.CreateTemp(ldsoconfdDir, pattern)
-	if err != nil {
-		return fmt.Errorf("failed to create config file: %w", err)
+	var configFile *os.File
+	if _, err := os.Stat(topLevelLdsoconfFilePath); os.IsNotExist(err) {
+		configFile, err = os.OpenFile(topLevelLdsoconfFilePath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0644)
+		if err != nil {
+			return fmt.Errorf("failed to open top-level ld.so.conf file: %w", err)
+		}
+	} else {
+		if err := os.MkdirAll(ldsoconfdDir, 0755); err != nil {
+			return fmt.Errorf("failed to create ld.so.conf.d: %w", err)
+		}
+		configFile, err = os.CreateTemp(ldsoconfdDir, pattern)
+		if err != nil {
+			return fmt.Errorf("failed to create config file: %w", err)
+		}
 	}
 	defer func() {
 		_ = configFile.Close()
@@ -205,7 +221,7 @@ func createLdsoconfdFile(pattern string, dirs ...string) error {
 		if added[dir] {
 			continue
 		}
-		_, err = fmt.Fprintf(configFile, "%s\n", dir)
+		_, err := fmt.Fprintf(configFile, "%s\n", dir)
 		if err != nil {
 			return fmt.Errorf("failed to update config file: %w", err)
 		}