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// Copyright 2018 Google LLC
//
// 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.googlesource.com/gvisor/pkg/sentry/context"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ashmem"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs/binder"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
"gvisor.googlesource.com/gvisor/pkg/sentry/fs/tmpfs"
"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
func newCharacterDevice(iops fs.InodeOperations, msrc *fs.MountSource) *fs.Inode {
return fs.NewInode(iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: usermem.PageSize,
Type: fs.CharacterDevice,
})
}
func newDirectory(ctx context.Context, msrc *fs.MountSource) *fs.Inode {
iops := ramfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0555))
return fs.NewInode(iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: usermem.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(iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: usermem.PageSize,
Type: fs.Symlink,
})
}
// New returns the root node of a device filesystem.
func New(ctx context.Context, msrc *fs.MountSource, binderEnabled bool, ashmemEnabled bool) *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": newCharacterDevice(newNullDevice(ctx, fs.RootOwner, 0666), msrc),
"zero": newCharacterDevice(newZeroDevice(ctx, fs.RootOwner, 0666), msrc),
"full": newCharacterDevice(newFullDevice(ctx, fs.RootOwner, 0666), msrc),
// 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": newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
"urandom": newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
"shm": tmpfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0777), msrc, kernel.KernelFromContext(ctx)),
// 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, 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),
}
if binderEnabled {
binder := binder.NewDevice(ctx, fs.RootOwner, fs.FilePermsFromMode(0666))
contents["binder"] = newCharacterDevice(binder, msrc)
}
if ashmemEnabled {
ashmem := ashmem.NewDevice(ctx, fs.RootOwner, fs.FilePermsFromMode(0666))
contents["ashmem"] = newCharacterDevice(ashmem, msrc)
}
iops := ramfs.NewDir(ctx, contents, fs.RootOwner, fs.FilePermsFromMode(0555))
return fs.NewInode(iops, msrc, fs.StableAttr{
DeviceID: devDevice.DeviceID(),
InodeID: devDevice.NextIno(),
BlockSize: usermem.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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