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|
package container
import (
"errors"
"fmt"
"os"
"path/filepath"
. "syscall"
"hakurei.app/container/vfs"
)
/*
Holding CAP_SYS_ADMIN within the user namespace that owns a process's mount namespace
allows that process to create bind mounts and mount the following types of filesystems:
- /proc (since Linux 3.8)
- /sys (since Linux 3.8)
- devpts (since Linux 3.9)
- tmpfs(5) (since Linux 3.9)
- ramfs (since Linux 3.9)
- mqueue (since Linux 3.9)
- bpf (since Linux 4.4)
- overlayfs (since Linux 5.11)
*/
const (
// zeroString is a zero value string, it represents NULL when passed to mount.
zeroString = ""
// SourceNone is used when the source value is ignored,
// such as when remounting.
SourceNone = "none"
// SourceProc is used when mounting proc.
// Note that any source value is allowed when fstype is [FstypeProc].
SourceProc = "proc"
// SourceDevpts is used when mounting devpts.
// Note that any source value is allowed when fstype is [FstypeDevpts].
SourceDevpts = "devpts"
// SourceMqueue is used when mounting mqueue.
// Note that any source value is allowed when fstype is [FstypeMqueue].
SourceMqueue = "mqueue"
// SourceTmpfsDevtmpfs is used when mounting tmpfs representing a subset of host devtmpfs.
SourceTmpfsDevtmpfs = "devtmpfs"
// SourceTmpfsEphemeral is used when mounting a writable instance of tmpfs.
SourceTmpfsEphemeral = "ephemeral"
// SourceTmpfsReadonly is used when mounting a readonly instance of tmpfs.
SourceTmpfsReadonly = "readonly"
// FstypeNULL is used when the fstype value is ignored,
// such as when bind mounting or remounting.
FstypeNULL = zeroString
// FstypeProc represents the proc pseudo-filesystem.
// A fully visible instance of proc must be available in the mount namespace for proc to be mounted.
// This filesystem type is usually mounted on /proc.
FstypeProc = "proc"
// FstypeDevpts represents the devpts pseudo-filesystem.
// This type of filesystem is usually mounted on /dev/pts.
FstypeDevpts = "devpts"
// FstypeTmpfs represents the tmpfs filesystem.
// This filesystem type can be mounted anywhere in the container filesystem.
FstypeTmpfs = "tmpfs"
// FstypeMqueue represents the mqueue pseudo-filesystem.
// This filesystem type is usually mounted on /dev/mqueue.
FstypeMqueue = "mqueue"
)
// bindMount mounts source on target and recursively applies flags if MS_REC is set.
func (p *procPaths) bindMount(source, target string, flags uintptr, eq bool) error {
if eq {
msg.Verbosef("resolved %q flags %#x", target, flags)
} else {
msg.Verbosef("resolved %q on %q flags %#x", source, target, flags)
}
if err := Mount(source, target, FstypeNULL, MS_SILENT|MS_BIND|flags&MS_REC, zeroString); err != nil {
return wrapErrSuffix(err,
fmt.Sprintf("cannot mount %q on %q:", source, target))
}
return p.remount(target, flags)
}
// remount applies flags on target, recursively if MS_REC is set.
func (p *procPaths) remount(target string, flags uintptr) error {
var targetFinal string
if v, err := filepath.EvalSymlinks(target); err != nil {
return wrapErrSelf(err)
} else {
targetFinal = v
if targetFinal != target {
msg.Verbosef("target resolves to %q", targetFinal)
}
}
// final target path according to the kernel through proc
var targetKFinal string
{
var destFd int
if err := IgnoringEINTR(func() (err error) {
destFd, err = Open(targetFinal, O_PATH|O_CLOEXEC, 0)
return
}); err != nil {
return wrapErrSuffix(err,
fmt.Sprintf("cannot open %q:", targetFinal))
}
if v, err := os.Readlink(p.fd(destFd)); err != nil {
return wrapErrSelf(err)
} else if err = Close(destFd); err != nil {
return wrapErrSuffix(err,
fmt.Sprintf("cannot close %q:", targetFinal))
} else {
targetKFinal = v
}
}
mf := MS_NOSUID | flags&MS_NODEV | flags&MS_RDONLY
return hostProc.mountinfo(func(d *vfs.MountInfoDecoder) error {
n, err := d.Unfold(targetKFinal)
if err != nil {
if errors.Is(err, ESTALE) {
return msg.WrapErr(err,
fmt.Sprintf("mount point %q never appeared in mountinfo", targetKFinal))
}
return wrapErrSuffix(err,
"cannot unfold mount hierarchy:")
}
if err = remountWithFlags(n, mf); err != nil {
return err
}
if flags&MS_REC == 0 {
return nil
}
for cur := range n.Collective() {
err = remountWithFlags(cur, mf)
if err != nil && !errors.Is(err, EACCES) {
return err
}
}
return nil
})
}
// remountWithFlags remounts mount point described by [vfs.MountInfoNode].
func remountWithFlags(n *vfs.MountInfoNode, mf uintptr) error {
kf, unmatched := n.Flags()
if len(unmatched) != 0 {
msg.Verbosef("unmatched vfs options: %q", unmatched)
}
if kf&mf != mf {
return wrapErrSuffix(
Mount(SourceNone, n.Clean, FstypeNULL, MS_SILENT|MS_BIND|MS_REMOUNT|kf|mf, zeroString),
fmt.Sprintf("cannot remount %q:", n.Clean))
}
return nil
}
func mountTmpfs(fsname, name string, flags uintptr, size int, perm os.FileMode) error {
target := toSysroot(name)
if err := os.MkdirAll(target, parentPerm(perm)); err != nil {
return wrapErrSelf(err)
}
opt := fmt.Sprintf("mode=%#o", perm)
if size > 0 {
opt += fmt.Sprintf(",size=%d", size)
}
return wrapErrSuffix(
Mount(fsname, target, FstypeTmpfs, flags, opt),
fmt.Sprintf("cannot mount tmpfs on %q:", name))
}
func parentPerm(perm os.FileMode) os.FileMode {
pperm := 0755
if perm&0070 == 0 {
pperm &= ^0050
}
if perm&0007 == 0 {
pperm &= ^0005
}
return os.FileMode(pperm)
}
|
