1 files changed, 135 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/ext/ext.go b/pkg/sentry/fsimpl/ext/ext.go
new file mode 100644
index 000000000..f10accafc
--- /dev/null
+++ b/pkg/sentry/fsimpl/ext/ext.go
@@ -0,0 +1,135 @@
+// 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/fsimpl/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
+}