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// Copyright (c) 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 fuse
import (
"fmt"
"os"
"os/exec"
"strings"
"github.com/sylabs/singularity/v4/internal/pkg/util/bin"
"github.com/sylabs/singularity/v4/pkg/image"
"github.com/sylabs/singularity/v4/pkg/sylog"
)
type ImageMount struct {
// Type represents what type of image this mount involves (from among the
// values in pkg/image)
Type int
// Readonly represents whether this is a Readonly overlay
Readonly bool
// SourcePath is the path of the image, stripped of any colon-prefixed
// options (like ":ro")
SourcePath string
// EnclosingDir is the location of a secure parent-directory in
// which to create the actual mountpoint directory
EnclosingDir string
// mountpoint is the directory at which the image will be mounted
mountpoint string
// AllowSetuid is set to true to mount the image the "nosuid" option.
AllowSetuid bool
// AllowDev is set to true to mount the image without the "nodev" option.
AllowDev bool
// AllowOther is set to true to mount the image with the "allow_other" option.
AllowOther bool
}
// Mount mounts an image to a temporary directory. It also verifies that
// the fusermount utility is present before performing the mount.
func (i *ImageMount) Mount() (err error) {
fuseMountCmd, err := i.determineMountCmd()
if err != nil {
return err
}
args, err := i.generateCmdArgs()
if err != nil {
return err
}
fuseCmdLine := fmt.Sprintf("%s %s", fuseMountCmd, strings.Join(args, " "))
sylog.Debugf("Executing FUSE mount command: %q", fuseCmdLine)
execCmd := exec.Command(fuseMountCmd, args...)
execCmd.Stderr = os.Stderr
_, err = execCmd.Output()
if err != nil {
return fmt.Errorf("encountered error while trying to mount image %q as overlay at %s: %w", i.SourcePath, i.mountpoint, err)
}
exitCode := execCmd.ProcessState.ExitCode()
if exitCode != 0 {
return fmt.Errorf("FUSE mount command %q returned non-zero exit code (%d)", fuseCmdLine, exitCode)
}
return err
}
func (i *ImageMount) determineMountCmd() (string, error) {
var fuseMountTool string
switch i.Type {
case image.SQUASHFS:
fuseMountTool = "squashfuse"
case image.EXT3:
fuseMountTool = "fuse2fs"
default:
return "", fmt.Errorf("image %q is not of a type that can be mounted with FUSE (type: %v)", i.SourcePath, i.Type)
}
fuseMountCmd, err := bin.FindBin(fuseMountTool)
if err != nil {
return "", fmt.Errorf("use of image %q as overlay requires %s to be installed: %w", i.SourcePath, fuseMountTool, err)
}
return fuseMountCmd, nil
}
func (i *ImageMount) generateCmdArgs() ([]string, error) {
args := make([]string, 0, 4)
switch i.Type {
case image.SQUASHFS:
i.Readonly = true
}
// Even though fusermount is not needed for this step, we shouldn't perform
// the mount unless we have the necessary tools to eventually unmount it
_, err := bin.FindBin("fusermount")
if err != nil {
return args, fmt.Errorf("use of image %q as overlay requires fusermount to be installed: %w", i.SourcePath, err)
}
if i.mountpoint == "" {
i.mountpoint, err = os.MkdirTemp(i.EnclosingDir, "mountpoint-")
if err != nil {
return args, fmt.Errorf("failed to create temporary dir %q for overlay %q: %w", i.mountpoint, i.SourcePath, err)
}
}
// Best effort to cleanup temporary dir
defer func() {
if err != nil {
sylog.Debugf("Encountered error with image %q; attempting to remove %q", i.SourcePath, i.mountpoint)
os.Remove(i.mountpoint)
}
}()
// TODO: Think through what makes sense for file ownership in FUSE-mounted
// images, vis a vis id-mappings and user-namespaces.
opts := []string{"uid=0", "gid=0"}
if i.Readonly {
// Not strictly necessary as will be read-only in assembled overlay,
// however this stops any erroneous writes through the stagingDir.
opts = append(opts, "ro")
}
// FUSE defaults to nosuid,nodev - attempt to reverse if AllowDev/Setuid requested.
if i.AllowDev {
opts = append(opts, "dev")
}
if i.AllowSetuid {
opts = append(opts, "suid")
}
if i.AllowOther {
opts = append(opts, "allow_other")
}
if len(opts) > 0 {
args = append(args, "-o", strings.Join(opts, ","))
}
args = append(args, i.SourcePath)
args = append(args, i.mountpoint)
return args, nil
}
func (i ImageMount) GetMountPoint() string {
return i.mountpoint
}
func (i *ImageMount) SetMountPoint(mountpoint string) {
i.mountpoint = mountpoint
}
func (i ImageMount) Unmount() error {
return UnmountWithFuse(i.GetMountPoint())
}
// UnmountWithFuse performs an unmount on the specified directory using
// fusermount -u.
func UnmountWithFuse(dir string) error {
fusermountCmd, err := bin.FindBin("fusermount")
if err != nil {
// We should not be creating FUSE-based mounts in the first place
// without checking that fusermount is available.
return fmt.Errorf("fusermount not available while trying to perform unmount: %w", err)
}
sylog.Debugf("Executing FUSE unmount command: %s -u %s", fusermountCmd, dir)
execCmd := exec.Command(fusermountCmd, "-u", dir)
execCmd.Stderr = os.Stderr
_, err = execCmd.Output()
return err
}
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