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// Copyright 2019 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 ext implements readonly ext(2/3/4) filesystems.
package ext
import (
"errors"
"fmt"
"io"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/fd"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/sentry/context"
"gvisor.dev/gvisor/pkg/sentry/fs/ext/disklayout"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/syserror"
)
// FilesystemType implements vfs.FilesystemType.
type FilesystemType struct{}
// Compiles only if FilesystemType implements vfs.FilesystemType.
var _ vfs.FilesystemType = (*FilesystemType)(nil)
// getDeviceFd returns an io.ReaderAt to the underlying device.
// Currently there are two ways of mounting an ext(2/3/4) fs:
// 1. Specify a mount with our internal special MountType in the OCI spec.
// 2. Expose the device to the container and mount it from application layer.
func getDeviceFd(source string, opts vfs.NewFilesystemOptions) (io.ReaderAt, error) {
if opts.InternalData == nil {
// User mount call.
// TODO(b/134676337): Open the device specified by `source` and return that.
panic("unimplemented")
}
// NewFilesystem call originated from within the sentry.
devFd, ok := opts.InternalData.(int)
if !ok {
return nil, errors.New("internal data for ext fs must be an int containing the file descriptor to device")
}
if devFd < 0 {
return nil, fmt.Errorf("ext device file descriptor is not valid: %d", devFd)
}
// The fd.ReadWriter returned from fd.NewReadWriter() does not take ownership
// of the file descriptor and hence will not close it when it is garbage
// collected.
return fd.NewReadWriter(devFd), nil
}
// isCompatible checks if the superblock has feature sets which are compatible.
// We only need to check the superblock incompatible feature set since we are
// mounting readonly. We will also need to check readonly compatible feature
// set when mounting for read/write.
func isCompatible(sb disklayout.SuperBlock) bool {
// Please note that what is being checked is limited based on the fact that we
// are mounting readonly and that we are not journaling. When mounting
// read/write or with a journal, this must be reevaluated.
incompatFeatures := sb.IncompatibleFeatures()
if incompatFeatures.MetaBG {
log.Warningf("ext fs: meta block groups are not supported")
return false
}
if incompatFeatures.MMP {
log.Warningf("ext fs: multiple mount protection is not supported")
return false
}
if incompatFeatures.Encrypted {
log.Warningf("ext fs: encrypted inodes not supported")
return false
}
if incompatFeatures.InlineData {
log.Warningf("ext fs: inline files not supported")
return false
}
return true
}
// NewFilesystem implements vfs.FilesystemType.NewFilesystem.
func (FilesystemType) NewFilesystem(ctx context.Context, creds *auth.Credentials, source string, opts vfs.NewFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
// TODO(b/134676337): Ensure that the user is mounting readonly. If not,
// EACCESS should be returned according to mount(2). Filesystem independent
// flags (like readonly) are currently not available in pkg/sentry/vfs.
dev, err := getDeviceFd(source, opts)
if err != nil {
return nil, nil, err
}
fs := filesystem{dev: dev, inodeCache: make(map[uint32]*inode)}
fs.vfsfs.Init(&fs)
fs.sb, err = readSuperBlock(dev)
if err != nil {
return nil, nil, err
}
if fs.sb.Magic() != linux.EXT_SUPER_MAGIC {
// mount(2) specifies that EINVAL should be returned if the superblock is
// invalid.
return nil, nil, syserror.EINVAL
}
// Refuse to mount if the filesystem is incompatible.
if !isCompatible(fs.sb) {
return nil, nil, syserror.EINVAL
}
fs.bgs, err = readBlockGroups(dev, fs.sb)
if err != nil {
return nil, nil, err
}
rootInode, err := fs.getOrCreateInodeLocked(disklayout.RootDirInode)
if err != nil {
return nil, nil, err
}
rootInode.incRef()
return &fs.vfsfs, &newDentry(rootInode).vfsd, nil
}
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