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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2018 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package syscheck
import (
"bytes"
"compress/gzip"
"encoding/base64"
"fmt"
"io"
"os"
"os/exec"
"path/filepath"
"github.com/snapcore/snapd/logger"
"github.com/snapcore/snapd/osutil"
"github.com/snapcore/snapd/osutil/squashfs"
"github.com/snapcore/snapd/sandbox/selinux"
)
func init() {
checks = append(checks, checkSquashfsMount)
}
// This image was created using:
//
// #!/bin/sh
//
// cd $(mktemp -d)
// cat > canary.txt<<'EOF'
// This file is used to check that snapd can read a squashfs image.
//
// The squashfs was generated with:
// EOF
// cat $0 >> canary.txt
//
// mksquashfs . /tmp/canary.squashfs -noappend -comp xz -no-xattrs -no-fragments >/dev/nul
// cat /tmp/canary.squashfs | gzip - | base64
var b64SquashfsImage = []byte(`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`)
var fuseBinary = "mount.fuse"
func firstCheckFuse() error {
if squashfs.NeedsFuse() {
if _, err := exec.LookPath(fuseBinary); err != nil {
return fmt.Errorf(`The "fuse" filesystem is required on this system but not available. Please try to install the fuse package.`)
}
}
return nil
}
func checkSquashfsMount() error {
if err := firstCheckFuse(); err != nil {
return err
}
tmpSquashfsFile, err := os.CreateTemp("", "syscheck-squashfs-")
if err != nil {
return err
}
defer os.Remove(tmpSquashfsFile.Name())
tmpMountDir, err := os.MkdirTemp("", "syscheck-mountpoint-")
if err != nil {
return err
}
defer os.RemoveAll(tmpMountDir)
// write the squashfs image
b64dec := base64.NewDecoder(base64.StdEncoding, bytes.NewBuffer(b64SquashfsImage))
gzReader, err := gzip.NewReader(b64dec)
if err != nil {
return err
}
if _, err := io.Copy(tmpSquashfsFile, gzReader); err != nil {
return err
}
// the fstype can be squashfs or fuse.{snap,squash}fuse
fstype, _ := squashfs.FsType()
options := []string{"-t", fstype}
if selinux.ProbedLevel() != selinux.Unsupported {
if ctx := selinux.SnapMountContext(); ctx != "" {
options = append(options, "-o", "context="+ctx)
}
}
options = append(options, tmpSquashfsFile.Name(), tmpMountDir)
cmd := exec.Command("mount", options...)
output, err := cmd.CombinedOutput()
if err != nil {
return fmt.Errorf("cannot mount squashfs image using %q: %v", fstype, osutil.OutputErr(output, err))
}
defer func() {
if output, err := exec.Command("umount", "-l", tmpMountDir).CombinedOutput(); err != nil {
// os.RemoveAll(tmpMountDir) will fail here if umount fails
logger.Noticef("cannot unmount syscheck check squashfs image: %v", osutil.OutputErr(output, err))
}
}()
// syscheck check the
content, err := os.ReadFile(filepath.Join(tmpMountDir, "canary.txt"))
if err != nil {
return fmt.Errorf("squashfs mount returned no err but canary file cannot be read")
}
if !bytes.HasPrefix(content, []byte("This file is used to check that snapd can read a squashfs image.")) {
return fmt.Errorf("unexpected squashfs canary content: %q", content)
}
return nil
}
|
