Allow internal reserved volumes on system mount paths

Author: cursoragent

lib/instances/create.go

@@ -658,6 +658,9 @@ func validateVolumeAttachments(attachments []VolumeAttachment, allowSystemVolume
 
 	seenPaths := make(map[string]bool)
 	for _, vol := range attachments {
+		reservedPrefix := volumes.ReservedVolumeIDPrefix(vol.VolumeID)
+		isReservedVolume := reservedPrefix != ""
+
 		// Validate mount path is absolute
 		if !filepath.IsAbs(vol.MountPath) {
 			return fmt.Errorf("volume %s: mount path %q must be absolute", vol.VolumeID, vol.MountPath)
@@ -666,16 +669,15 @@ func validateVolumeAttachments(attachments []VolumeAttachment, allowSystemVolume
 		// Clean the path to normalize it
 		cleanPath := filepath.Clean(vol.MountPath)
 
-		// Check for system directories
-		if isSystemDirectory(cleanPath) {
+		// Check for system directories. Internal instances may only bypass this
+		// restriction when attaching reserved internal volumes.
+		if isSystemDirectory(cleanPath) && !(allowSystemVolumes && isReservedVolume) {
 			return fmt.Errorf("volume %s: cannot mount to system directory %q", vol.VolumeID, cleanPath)
 		}
 
 		// Reserved internal volume IDs are attachable only by internal instances
-		if !allowSystemVolumes {
-			if prefix := volumes.ReservedVolumeIDPrefix(vol.VolumeID); prefix != "" {
-				return fmt.Errorf("volume %s: volume IDs with the prefix %q are reserved for internal use", vol.VolumeID, prefix)
-			}
+		if !allowSystemVolumes && isReservedVolume {
+			return fmt.Errorf("volume %s: volume IDs with the prefix %q are reserved for internal use", vol.VolumeID, reservedPrefix)
 		}
 
 		// Check for duplicate mount paths

lib/instances/resource_limits_test.go

@@ -251,4 +251,19 @@ func TestValidateVolumeAttachments_ReservedVolumeID(t *testing.T) {
 		MountPath: "/mnt/data",
 	}}, false)
 	assert.NoError(t, err)
+
+	// Internal instances may mount reserved internal volumes under system paths.
+	err = validateVolumeAttachments([]VolumeAttachment{{
+		VolumeID:  "builder-disk-abc123",
+		MountPath: "/var/lib/buildkit",
+	}}, true)
+	assert.NoError(t, err)
+
+	// The system-path bypass does not apply to non-reserved volume IDs.
+	err = validateVolumeAttachments([]VolumeAttachment{{
+		VolumeID:  "vol-1",
+		MountPath: "/var/lib/buildkit",
+	}}, true)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "system directory")
 }