Function validateOpenFDs

runsc/cmd/boot.go:700–743

validateOpenFDs checks that the sandbox process does not have any open directory FDs.

(passFDs []boot.FDMapping)

// validateOpenFDs checks that the sandbox process does not have any open
// directory FDs.
func validateOpenFDs(passFDs []boot.FDMapping) {
	passHostFDs := make(map[int]struct{})
	for _, passFD := range passFDs {
		passHostFDs[passFD.Host] = struct{}{}
	}
	const selfFDDir = "/proc/self/fd"
	if err := filepath.WalkDir(selfFDDir, func(path string, d os.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.Type() != os.ModeSymlink {
			// All entries are symlinks. Ignore the callback for fd directory itself.
			return nil
		}
		if fdInfo, err := os.Stat(path); err != nil {
			if os.IsNotExist(err) {
				// Ignore FDs that are now closed. For example, the FD to selfFDDir that
				// was opened by filepath.WalkDir() to read dirents.
				return nil
			}
			return fmt.Errorf("os.Stat(%s) failed: %v", path, err)
		} else if !fdInfo.IsDir() {
			return nil
		}
		// Uh-oh. This is a directory FD.
		fdNo, err := strconv.Atoi(d.Name())
		if err != nil {
			return fmt.Errorf("strconv.Atoi(%s) failed: %v", d.Name(), err)
		}
		dirLink, err := os.Readlink(path)
		if err != nil {
			return fmt.Errorf("os.Readlink(%s) failed: %v", path, err)
		}
		if _, ok := passHostFDs[fdNo]; ok {
			// Passed FDs are allowed to be directories. The user must be knowing
			// what they are doing. Log a warning regardless.
			log.Warningf("Sandbox has access to FD %d, which is a directory for %s", fdNo, dirLink)
			return nil
		}
		return fmt.Errorf("FD %d is a directory for %s", fdNo, dirLink)
	}); err != nil {
		util.Fatalf("WalkDir(%s) failed: %v", selfFDDir, err)
	}
}

// exportFinalMetrics exports all metrics to the given file.
// The file is closed as part of this function.