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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package dev provides a filesystem with simple devices.
package dev
import (
"math"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/fs/ramfs"
"gvisor.dev/gvisor/pkg/sentry/fs/tmpfs"
"gvisor.dev/gvisor/pkg/sentry/inet"
"gvisor.dev/gvisor/pkg/usermem"
)
// Memory device numbers are from Linux's drivers/char/mem.c
const (
// Mem device major.
memDevMajor uint16 = 1
// Mem device minors.
nullDevMinor uint32 = 3
zeroDevMinor uint32 = 5
fullDevMinor uint32 = 7
randomDevMinor uint32 = 8
urandomDevMinor uint32 = 9
)
// TTY major device number comes from include/uapi/linux/major.h.
const (
ttyDevMinor = 0
ttyDevMajor = 5
)
func newCharacterDevice(ctx context.Context, iops fs.InodeOperations, msrc *fs.MountSource, major uint16, minor uint32) *fs.Inode {
return fs.NewInode(ctx, iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: hostarch.PageSize,
Type: fs.CharacterDevice,
DeviceFileMajor: major,
DeviceFileMinor: minor,
})
}
func newMemDevice(ctx context.Context, iops fs.InodeOperations, msrc *fs.MountSource, minor uint32) *fs.Inode {
return fs.NewInode(ctx, iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: hostarch.PageSize,
Type: fs.CharacterDevice,
DeviceFileMajor: memDevMajor,
DeviceFileMinor: minor,
})
}
func newDirectory(ctx context.Context, contents map[string]*fs.Inode, msrc *fs.MountSource) *fs.Inode {
iops := ramfs.NewDir(ctx, contents, fs.RootOwner, fs.FilePermsFromMode(0555))
return fs.NewInode(ctx, iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: hostarch.PageSize,
Type: fs.Directory,
})
}
func newSymlink(ctx context.Context, target string, msrc *fs.MountSource) *fs.Inode {
iops := ramfs.NewSymlink(ctx, fs.RootOwner, target)
return fs.NewInode(ctx, iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: hostarch.PageSize,
Type: fs.Symlink,
})
}
// New returns the root node of a device filesystem.
func New(ctx context.Context, msrc *fs.MountSource) *fs.Inode {
contents := map[string]*fs.Inode{
"fd": newSymlink(ctx, "/proc/self/fd", msrc),
"stdin": newSymlink(ctx, "/proc/self/fd/0", msrc),
"stdout": newSymlink(ctx, "/proc/self/fd/1", msrc),
"stderr": newSymlink(ctx, "/proc/self/fd/2", msrc),
"null": newMemDevice(ctx, newNullDevice(ctx, fs.RootOwner, 0666), msrc, nullDevMinor),
"zero": newMemDevice(ctx, newZeroDevice(ctx, fs.RootOwner, 0666), msrc, zeroDevMinor),
"full": newMemDevice(ctx, newFullDevice(ctx, fs.RootOwner, 0666), msrc, fullDevMinor),
// This is not as good as /dev/random in linux because go
// runtime uses sys_random and /dev/urandom internally.
// According to 'man 4 random', this will be sufficient unless
// application uses this to generate long-lived GPG/SSL/SSH
// keys.
"random": newMemDevice(ctx, newRandomDevice(ctx, fs.RootOwner, 0444), msrc, randomDevMinor),
"urandom": newMemDevice(ctx, newRandomDevice(ctx, fs.RootOwner, 0444), msrc, urandomDevMinor),
"shm": tmpfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0777), msrc),
// A devpts is typically mounted at /dev/pts to provide
// pseudoterminal support. Place an empty directory there for
// the devpts to be mounted over.
"pts": newDirectory(ctx, nil, msrc),
// Similarly, applications expect a ptmx device at /dev/ptmx
// connected to the terminals provided by /dev/pts/. Rather
// than creating a device directly (which requires a hairy
// lookup on open to determine if a devpts exists), just create
// a symlink to the ptmx provided by devpts. (The Linux devpts
// documentation recommends this).
//
// If no devpts is mounted, this will simply be a dangling
// symlink, which is fine.
"ptmx": newSymlink(ctx, "pts/ptmx", msrc),
"tty": newCharacterDevice(ctx, newTTYDevice(ctx, fs.RootOwner, 0666), msrc, ttyDevMajor, ttyDevMinor),
}
if isNetTunSupported(inet.StackFromContext(ctx)) {
contents["net"] = newDirectory(ctx, map[string]*fs.Inode{
"tun": newCharacterDevice(ctx, newNetTunDevice(ctx, fs.RootOwner, 0666), msrc, netTunDevMajor, netTunDevMinor),
}, msrc)
}
iops := ramfs.NewDir(ctx, contents, fs.RootOwner, fs.FilePermsFromMode(0555))
return fs.NewInode(ctx, iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: hostarch.PageSize,
Type: fs.Directory,
})
}
// readZeros implements fs.FileOperations.Read with infinite null bytes.
type readZeros struct{}
// Read implements fs.FileOperations.Read.
func (*readZeros) Read(ctx context.Context, file *fs.File, dst usermem.IOSequence, offset int64) (int64, error) {
return dst.ZeroOut(ctx, math.MaxInt64)
}
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