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// Copyright (c) 2019-2023, Sylabs Inc. All rights reserved.
// This software is licensed under a 3-clause BSD license. Please consult the
// LICENSE.md file distributed with the sources of this project regarding your
// rights to use or distribute this software.
package ociimage
import (
"archive/tar"
"bufio"
"compress/gzip"
"context"
"fmt"
"io"
"net/http"
"os"
"path/filepath"
"strings"
"github.com/containers/image/v5/copy"
ocilayout "github.com/containers/image/v5/oci/layout"
"github.com/containers/image/v5/types"
"github.com/opencontainers/go-digest"
"github.com/sylabs/singularity/v4/internal/pkg/cache"
"github.com/sylabs/singularity/v4/pkg/sylog"
"golang.org/x/term"
)
// FetchLayout will fetch the OCI image specified by imageRef to a containers/image OCI layout in layoutDir.
// An ImageReference to the image that was fetched into layoutDir is returned on success.
// If imgCache is non-nil, and enabled, the image will be pulled through the cache.
func FetchLayout(ctx context.Context, sysCtx *types.SystemContext, imgCache *cache.Handle, imageRef, layoutDir string) (types.ImageReference, digest.Digest, error) {
policyCtx, err := defaultPolicy()
if err != nil {
return nil, "", err
}
srcRef, err := ParseImageRef(imageRef)
if err != nil {
return nil, "", fmt.Errorf("invalid image source: %v", err)
}
// oci-archive direct handling by containers/image can fail as non-root.
// Perform a tar extraction first, and handle as an oci layout.
if os.Geteuid() != 0 && srcRef.Transport().Name() == "oci-archive" {
var tmpDir string
tmpDir, err = os.MkdirTemp(sysCtx.BigFilesTemporaryDir, "temp-oci-")
if err != nil {
return nil, "", fmt.Errorf("could not create temporary oci directory: %v", err)
}
defer os.RemoveAll(tmpDir)
archiveParts := strings.SplitN(srcRef.StringWithinTransport(), ":", 2)
sylog.Debugf("Extracting oci-archive %q to %q", archiveParts[0], tmpDir)
err = extractArchive(archiveParts[0], tmpDir)
if err != nil {
return nil, "", fmt.Errorf("error extracting the OCI archive file: %v", err)
}
// We may or may not have had a ':tag' in the source to handle
if len(archiveParts) == 2 {
srcRef, err = ocilayout.ParseReference(tmpDir + ":" + archiveParts[1])
} else {
srcRef, err = ocilayout.ParseReference(tmpDir)
}
if err != nil {
return nil, "", err
}
}
var imgDigest digest.Digest
if imgCache != nil && !imgCache.IsDisabled() {
// Grab the modified source ref from the cache
srcRef, imgDigest, err = CacheReference(ctx, sysCtx, imgCache, srcRef)
if err != nil {
return nil, "", err
}
}
lr, err := ocilayout.ParseReference(layoutDir + ":" + imgDigest.String())
if err != nil {
return nil, "", err
}
copyOpts := copy.Options{
ReportWriter: os.Stdout,
SourceCtx: sysCtx,
}
if (sylog.GetLevel() <= -1) || !term.IsTerminal(2) {
copyOpts.ReportWriter = io.Discard
}
_, err = copy.Image(ctx, policyCtx, lr, srcRef, ©Opts)
if err != nil {
return nil, "", err
}
return lr, imgDigest, nil
}
// Perform a dumb tar(gz) extraction with no chown, id remapping etc.
// This is needed for non-root handling of `oci-archive` as the extraction
// by containers/archive is failing when uid/gid don't match local machine
// and we're not root
func extractArchive(src string, dst string) error {
f, err := os.Open(src)
if err != nil {
return err
}
defer f.Close()
r := bufio.NewReader(f)
header, err := r.Peek(10) // read a few bytes without consuming
if err != nil {
return err
}
gzipped := strings.Contains(http.DetectContentType(header), "x-gzip")
if gzipped {
r, err := gzip.NewReader(f)
if err != nil {
return err
}
defer r.Close()
}
tr := tar.NewReader(r)
for {
header, err := tr.Next()
switch {
// if no more files are found return
case err == io.EOF:
return nil
// return any other error
case err != nil:
return err
// if the header is nil, just skip it (not sure how this happens)
case header == nil:
continue
}
// ZipSlip protection - don't escape from dst
//#nosec G305
target := filepath.Join(dst, header.Name)
if !strings.HasPrefix(target, filepath.Clean(dst)+string(os.PathSeparator)) {
return fmt.Errorf("%s: illegal extraction path", target)
}
// check the file type
switch header.Typeflag {
// if its a dir and it doesn't exist create it
case tar.TypeDir:
if _, err := os.Stat(target); err != nil {
if err := os.MkdirAll(target, 0o755); err != nil {
return err
}
}
// if it's a file create it
case tar.TypeReg:
f, err := os.OpenFile(target, os.O_CREATE|os.O_RDWR, os.FileMode(header.Mode))
if err != nil {
return err
}
defer f.Close()
// copy over contents
//#nosec G110
if _, err := io.Copy(f, tr); err != nil {
return err
}
}
}
}
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