1 files changed, 131 insertions, 0 deletions
diff --git a/pkg/sentry/fs/tmpfs/fs.go b/pkg/sentry/fs/tmpfs/fs.go
new file mode 100644
index 000000000..639a19b0d
--- /dev/null
+++ b/pkg/sentry/fs/tmpfs/fs.go
@@ -0,0 +1,131 @@
+// Copyright 2018 Google Inc.
+//
+// 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"
+	"regexp"
+	"strconv"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+)
+
+const (
+	// Set initial permissions for the root directory.
+	modeKey = "mode"
+
+	// UID for the root directory.
+	rootUIDKey = "uid"
+
+	// GID for the root directory.
+	rootGIDKey = "gid"
+
+	// TODO: support a tmpfs size limit.
+	// size = "size"
+
+	// default permissions are read/write/execute.
+	defaultMode = 0777
+)
+
+// modeRegexp is the expected format of the mode option.
+var modeRegexp = regexp.MustCompile("0[0-7][0-7][0-7]")
+
+// Filesystem is a tmpfs.
+type Filesystem struct{}
+
+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
+}
+
+// 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) (*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 {
+		if !modeRegexp.MatchString(m) {
+			return nil, fmt.Errorf("unsupported mode value: 'mode=%s'", m)
+		}
+		// It's basically impossible that we error out at this point,
+		// maybe we should panic.
+		i, err := strconv.ParseUint(m, 8, 32)
+		if err != nil {
+			return nil, fmt.Errorf("mode value not parsable 'mode=%s': %v", m, err)
+		}
+		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)
+	}
+
+	// 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 a mount which will cache dirents.
+	msrc := fs.NewCachingMountSource(f, flags)
+
+	// Construct the tmpfs root.
+	return NewDir(ctx, nil, owner, perms, msrc, platform.FromContext(ctx)), nil
+}