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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 tmpfs
import (
"fmt"
"strconv"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
)
const (
// Set initial permissions for the root directory.
modeKey = "mode"
// UID for the root directory.
rootUIDKey = "uid"
// GID for the root directory.
rootGIDKey = "gid"
// cacheKey sets the caching policy for the mount.
cacheKey = "cache"
// cacheAll uses the virtual file system cache for everything (default).
cacheAll = "cache"
// cacheRevalidate allows dirents to be cached, but revalidates them on each
// lookup.
cacheRevalidate = "revalidate"
// TODO(edahlgren/mpratt): support a tmpfs size limit.
// size = "size"
// Permissions that exceed modeMask will be rejected.
modeMask = 01777
// Default permissions are read/write/execute.
defaultMode = 0777
)
// Filesystem is a tmpfs.
//
// +stateify savable
type Filesystem struct{}
var _ fs.Filesystem = (*Filesystem)(nil)
func init() {
fs.RegisterFilesystem(&Filesystem{})
}
// FilesystemName is the name underwhich the filesystem is registered.
// Name matches mm/shmem.c:shmem_fs_type.name.
const FilesystemName = "tmpfs"
// Name is the name of the file system.
func (*Filesystem) Name() string {
return FilesystemName
}
// AllowUserMount allows users to mount(2) this file system.
func (*Filesystem) AllowUserMount() bool {
return true
}
// AllowUserList allows this filesystem to be listed in /proc/filesystems.
func (*Filesystem) AllowUserList() bool {
return true
}
// Flags returns that there is nothing special about this file system.
//
// In Linux, tmpfs returns FS_USERNS_MOUNT, see mm/shmem.c.
func (*Filesystem) Flags() fs.FilesystemFlags {
return 0
}
// Mount returns a tmpfs root that can be positioned in the vfs.
func (f *Filesystem) Mount(ctx context.Context, device string, flags fs.MountSourceFlags, data string, _ interface{}) (*fs.Inode, error) {
// device is always ignored.
// Parse generic comma-separated key=value options, this file system expects them.
options := fs.GenericMountSourceOptions(data)
// Parse the root directory permissions.
perms := fs.FilePermsFromMode(defaultMode)
if m, ok := options[modeKey]; ok {
i, err := strconv.ParseUint(m, 8, 32)
if err != nil {
return nil, fmt.Errorf("mode value not parsable 'mode=%s': %v", m, err)
}
if i&^modeMask != 0 {
return nil, fmt.Errorf("invalid mode %q: must be less than %o", m, modeMask)
}
perms = fs.FilePermsFromMode(linux.FileMode(i))
delete(options, modeKey)
}
creds := auth.CredentialsFromContext(ctx)
owner := fs.FileOwnerFromContext(ctx)
if uidstr, ok := options[rootUIDKey]; ok {
uid, err := strconv.ParseInt(uidstr, 10, 32)
if err != nil {
return nil, fmt.Errorf("uid value not parsable 'uid=%d': %v", uid, err)
}
owner.UID = creds.UserNamespace.MapToKUID(auth.UID(uid))
delete(options, rootUIDKey)
}
if gidstr, ok := options[rootGIDKey]; ok {
gid, err := strconv.ParseInt(gidstr, 10, 32)
if err != nil {
return nil, fmt.Errorf("gid value not parsable 'gid=%d': %v", gid, err)
}
owner.GID = creds.UserNamespace.MapToKGID(auth.GID(gid))
delete(options, rootGIDKey)
}
// Construct a mount which will follow the cache options provided.
var msrc *fs.MountSource
switch options[cacheKey] {
case "", cacheAll:
msrc = fs.NewCachingMountSource(f, flags)
case cacheRevalidate:
msrc = fs.NewRevalidatingMountSource(f, flags)
default:
return nil, fmt.Errorf("invalid cache policy option %q", options[cacheKey])
}
delete(options, cacheKey)
// Fail if the caller passed us more options than we can parse. They may be
// expecting us to set something we can't set.
if len(options) > 0 {
return nil, fmt.Errorf("unsupported mount options: %v", options)
}
// Construct the tmpfs root.
return NewDir(ctx, nil, owner, perms, msrc), nil
}
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