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package microvm
import ( "bufio" "fmt" "io" "path/filepath" "regexp" "strconv" "strings")
type narinfo struct { StorePath string URL string NarHash string NarSize int64 // paths this path depends on References []string}
const ( maxNarinfoSize = 1 << 20 // 1 MiB storePrefix = "/nix/store/" maxNarinfoLineLen = maxNarinfoSize)
var nixStorePathBaseRe = regexp.MustCompile(`^[0-9abcdfghijklmnpqrsvwxyz]{32}-[^/]+$`)
// parseNarinfo parses and validates a narinfo body.// - required fields must be present// - StorePath must be under /nix/store/// - URL must be a relative, traversal-safe path referencing a NAR in the// same staging cache// - NarSize must be a non-negative integerfunc parseNarinfo(r io.Reader) (*narinfo, error) { lr := io.LimitReader(r, maxNarinfoSize+1) scanner := bufio.NewScanner(lr) scanner.Buffer(make([]byte, 4096), maxNarinfoLineLen)
var info narinfo for scanner.Scan() { line := scanner.Text() if line == "" { continue } key, value, ok := strings.Cut(line, ":") if !ok { return nil, fmt.Errorf("invalid narinfo line %q", line) } key = strings.TrimSpace(key) value = strings.TrimSpace(value)
switch key { case "StorePath": info.StorePath = value case "URL": info.URL = value case "NarHash": info.NarHash = value case "NarSize": n, err := strconv.ParseInt(value, 10, 64) if err != nil { return nil, fmt.Errorf("invalid NarSize %q: %w", value, err) } info.NarSize = n case "References": info.References = strings.Fields(value) } } if err := scanner.Err(); err != nil { return nil, fmt.Errorf("read narinfo: %w", err) }
if err := validateNarinfo(&info); err != nil { return nil, err } return &info, nil}
func validateNarinfo(info *narinfo) error { if info.StorePath == "" { return fmt.Errorf("narinfo missing StorePath") } if _, _, err := parseStorePath(info.StorePath); err != nil { return fmt.Errorf("invalid StorePath: %w", err) } if info.URL == "" { return fmt.Errorf("narinfo missing URL") } if strings.HasPrefix(info.URL, "/") || strings.Contains(info.URL, "..") { return fmt.Errorf("narinfo URL %q is not a safe relative path", info.URL) } if !strings.HasPrefix(info.URL, "nar/") { return fmt.Errorf("narinfo URL %q must reference a staged nar/ object", info.URL) } name := strings.TrimPrefix(info.URL, "nar/") if name == "" || name == "." || name != filepath.Base(name) || strings.Contains(name, "/") { return fmt.Errorf("narinfo URL %q is not a safe nar object path", info.URL) } if info.NarHash == "" { return fmt.Errorf("narinfo missing NarHash") } if info.NarSize < 0 { return fmt.Errorf("narinfo NarSize must be non-negative") } return nil}
func parseStorePath(path string) (hash string, name string, err error) { if !strings.HasPrefix(path, storePrefix) { return "", "", fmt.Errorf("store path %q does not start with %q", path, storePrefix) }
base := strings.TrimPrefix(path, storePrefix) if base == "" || strings.Contains(base, "/") { return "", "", fmt.Errorf("store path %q has invalid base name", path) } if !nixStorePathBaseRe.MatchString(base) { return "", "", fmt.Errorf("store path %q is not a valid nix store path", path) }
hash, name, ok := strings.Cut(base, "-") if !ok || hash == "" || name == "" { return "", "", fmt.Errorf("store path %q is missing hash or name", path) } return hash, name, nil}