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|
//go:build linux && composefs && cgo
// +build linux,composefs,cgo
package overlay
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io/fs"
"os"
"os/exec"
"path/filepath"
"sync"
"syscall"
"unsafe"
"github.com/containers/storage/pkg/loopback"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
var (
composeFsHelperOnce sync.Once
composeFsHelperPath string
composeFsHelperErr error
)
func getComposeFsHelper() (string, error) {
composeFsHelperOnce.Do(func() {
composeFsHelperPath, composeFsHelperErr = exec.LookPath("composefs-from-json")
})
return composeFsHelperPath, composeFsHelperErr
}
func composeFsSupported() bool {
_, err := getComposeFsHelper()
return err == nil
}
func enableVerity(description string, fd int) error {
enableArg := unix.FsverityEnableArg{
Version: 1,
Hash_algorithm: unix.FS_VERITY_HASH_ALG_SHA256,
Block_size: 4096,
}
_, _, e1 := syscall.Syscall(unix.SYS_IOCTL, uintptr(fd), uintptr(unix.FS_IOC_ENABLE_VERITY), uintptr(unsafe.Pointer(&enableArg)))
if e1 != 0 && !errors.Is(e1, unix.EEXIST) {
return fmt.Errorf("failed to enable verity for %q: %w", description, e1)
}
return nil
}
func enableVerityRecursive(path string) error {
walkFn := func(path string, d fs.DirEntry, err error) error {
if err != nil {
return err
}
if !d.Type().IsRegular() {
return nil
}
f, err := os.Open(path)
if err != nil {
return err
}
defer f.Close()
if err := enableVerity(path, int(f.Fd())); err != nil {
return err
}
return nil
}
return filepath.WalkDir(path, walkFn)
}
func getComposefsBlob(dataDir string) string {
return filepath.Join(dataDir, "composefs.blob")
}
func generateComposeFsBlob(toc []byte, composefsDir string) error {
if err := os.MkdirAll(composefsDir, 0o700); err != nil {
return err
}
destFile := getComposefsBlob(composefsDir)
writerJson, err := getComposeFsHelper()
if err != nil {
return fmt.Errorf("failed to find composefs-from-json: %w", err)
}
fd, err := unix.Openat(unix.AT_FDCWD, destFile, unix.O_WRONLY|unix.O_CREAT|unix.O_TRUNC|unix.O_EXCL|unix.O_CLOEXEC, 0o644)
if err != nil {
return fmt.Errorf("failed to open output file: %w", err)
}
outFd := os.NewFile(uintptr(fd), "outFd")
fd, err = unix.Open(fmt.Sprintf("/proc/self/fd/%d", outFd.Fd()), unix.O_RDONLY|unix.O_CLOEXEC, 0)
if err != nil {
outFd.Close()
return fmt.Errorf("failed to dup output file: %w", err)
}
newFd := os.NewFile(uintptr(fd), "newFd")
defer newFd.Close()
err = func() error {
// a scope to close outFd before setting fsverity on the read-only fd.
defer outFd.Close()
cmd := exec.Command(writerJson, "--format=erofs", "--out=/proc/self/fd/3", "/proc/self/fd/0")
cmd.ExtraFiles = []*os.File{outFd}
cmd.Stderr = os.Stderr
cmd.Stdin = bytes.NewReader(toc)
if err := cmd.Run(); err != nil {
return fmt.Errorf("failed to convert json to erofs: %w", err)
}
return nil
}()
if err != nil {
return err
}
if err := enableVerity("manifest file", int(newFd.Fd())); err != nil && !errors.Is(err, unix.ENOTSUP) && !errors.Is(err, unix.ENOTTY) {
logrus.Warningf("%s", err)
}
return nil
}
/*
typedef enum {
LCFS_EROFS_FLAGS_HAS_ACL = (1 << 0),
} lcfs_erofs_flag_t;
struct lcfs_erofs_header_s {
uint32_t magic;
uint32_t version;
uint32_t flags;
uint32_t unused[5];
} __attribute__((__packed__));
*/
// hasACL returns true if the erofs blob has ACLs enabled
func hasACL(path string) (bool, error) {
const LCFS_EROFS_FLAGS_HAS_ACL = (1 << 0)
fd, err := unix.Openat(unix.AT_FDCWD, path, unix.O_RDONLY|unix.O_CLOEXEC, 0)
if err != nil {
return false, err
}
defer unix.Close(fd)
// do not worry about checking the magic number, if the file is invalid
// we will fail to mount it anyway
flags := make([]byte, 4)
nread, err := unix.Pread(fd, flags, 8)
if err != nil {
return false, err
}
if nread != 4 {
return false, fmt.Errorf("failed to read flags from %q", path)
}
return binary.LittleEndian.Uint32(flags)&LCFS_EROFS_FLAGS_HAS_ACL != 0, nil
}
func mountComposefsBlob(dataDir, mountPoint string) error {
blobFile := getComposefsBlob(dataDir)
loop, err := loopback.AttachLoopDevice(blobFile)
if err != nil {
return err
}
defer loop.Close()
hasACL, err := hasACL(blobFile)
if err != nil {
return err
}
mountOpts := "ro"
if !hasACL {
mountOpts += ",noacl"
}
return unix.Mount(loop.Name(), mountPoint, "erofs", unix.MS_RDONLY, mountOpts)
}
|
