internal/pkg: validate tar pathnames

TContext no longer validates FileArtifact ahead of time, validation outcome is instead determined after consuming the reader to EOF. All data must therefore be treated as untrusted input until the reader is closed.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar.go

@@ -10,8 +10,7 @@ import (
 	"io/fs"
 	"net/http"
 	"os"
-
-	"hakurei.app/container/check"
+	"path"
 )
 
 const (
@@ -100,7 +99,6 @@ func (e DisallowedTypeflagError) Error() string {
 
 // Cure cures the [Artifact], producing a directory located at work.
 func (a *tarArtifact) Cure(t *TContext) (err error) {
-	temp := t.GetTempDir()
 	var tr io.ReadCloser
 	if tr, err = t.Open(a.f); err != nil {
 		return
@@ -137,14 +135,24 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 	}
 
 	type dirTargetPerm struct {
-		path *check.Absolute
+		path string
 		mode fs.FileMode
 	}
 	var madeDirectories []dirTargetPerm
 
-	if err = os.MkdirAll(temp.String(), 0700); err != nil {
+	if err = os.MkdirAll(t.GetTempDir().String(), 0700); err != nil {
 		return
 	}
+	var root *os.Root
+	if root, err = os.OpenRoot(t.GetTempDir().String()); err != nil {
+		return
+	}
+	defer func() {
+		closeErr := root.Close()
+		if err == nil {
+			err = closeErr
+		}
+	}()
 
 	var header *tar.Header
 	r := tar.NewReader(tr)
@@ -158,9 +166,8 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 			}
 		}
 
-		pathname := temp.Append(header.Name)
 		if typeflag >= '0' && typeflag <= '9' && typeflag != tar.TypeDir {
-			if err = os.MkdirAll(pathname.Dir().String(), 0700); err != nil {
+			if err = root.MkdirAll(path.Dir(header.Name), 0700); err != nil {
 				return
 			}
 		}
@@ -168,8 +175,8 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 		switch typeflag {
 		case tar.TypeReg:
 			var f *os.File
-			if f, err = os.OpenFile(
-				pathname.String(),
+			if f, err = root.OpenFile(
+				header.Name,
 				os.O_CREATE|os.O_EXCL|os.O_WRONLY,
 				header.FileInfo().Mode()&0500,
 			); err != nil {
@@ -184,26 +191,29 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 			break
 
 		case tar.TypeLink:
-			if err = os.Link(
-				temp.Append(header.Linkname).String(),
-				pathname.String(),
+			if err = root.Link(
+				header.Linkname,
+				header.Name,
 			); err != nil {
 				return
 			}
 			break
 
 		case tar.TypeSymlink:
-			if err = os.Symlink(header.Linkname, pathname.String()); err != nil {
+			if err = root.Symlink(
+				header.Linkname,
+				header.Name,
+			); err != nil {
 				return
 			}
 			break
 
 		case tar.TypeDir:
 			madeDirectories = append(madeDirectories, dirTargetPerm{
-				path: pathname,
+				path: header.Name,
 				mode: header.FileInfo().Mode(),
 			})
-			if err = os.MkdirAll(pathname.String(), 0700); err != nil {
+			if err = root.MkdirAll(header.Name, 0700); err != nil {
 				return
 			}
 			break
@@ -220,7 +230,7 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 	}
 	if err == nil {
 		for _, e := range madeDirectories {
-			if err = os.Chmod(e.path.String(), e.mode&0500); err != nil {
+			if err = root.Chmod(e.path, e.mode&0500); err != nil {
 				return
 			}
 		}
@@ -228,6 +238,7 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 		return
 	}
 
+	temp := t.GetTempDir()
 	if err = os.Chmod(temp.String(), 0700); err != nil {
 		return
 	}