3 files changed, 81 insertions, 2 deletions
diff --git a/pkg/sentry/fsimpl/fuse/BUILD b/pkg/sentry/fsimpl/fuse/BUILD
index a6ee6100d..86dc6a7a4 100644
--- a/pkg/sentry/fsimpl/fuse/BUILD
+++ b/pkg/sentry/fsimpl/fuse/BUILD
@@ -40,6 +40,7 @@ go_library(
         "register.go",
         "regular_file.go",
         "request_list.go",
+        "request_response.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
diff --git a/pkg/sentry/fsimpl/fuse/init.go b/pkg/sentry/fsimpl/fuse/init.go
index 6384cbbdb..256b6fb65 100644
--- a/pkg/sentry/fsimpl/fuse/init.go
+++ b/pkg/sentry/fsimpl/fuse/init.go
@@ -76,12 +76,12 @@ func (conn *connection) InitRecv(res *Response, hasSysAdminCap bool) error {
 		return err
 	}
 
-	initRes := linux.FUSEInitRes{Len: res.DataLen()}
+	initRes := fuseInitRes{initLen: res.DataLen()}
 	if err := res.UnmarshalPayload(&initRes); err != nil {
 		return err
 	}
 
-	return conn.initProcessReply(&initRes.InitOut, hasSysAdminCap)
+	return conn.initProcessReply(&initRes.initOut, hasSysAdminCap)
 }
 
 // Process the FUSE_INIT reply from the FUSE server.
diff --git a/pkg/sentry/fsimpl/fuse/request_response.go b/pkg/sentry/fsimpl/fuse/request_response.go
new file mode 100644
index 000000000..ae71b5e28
--- /dev/null
+++ b/pkg/sentry/fsimpl/fuse/request_response.go
@@ -0,0 +1,78 @@
+// Copyright 2020 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 fuse
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/tools/go_marshal/marshal"
+)
+
+// fuseInitRes is a variable-length wrapper of linux.FUSEInitOut. The FUSE
+// server may implement an older version of FUSE protocol, which contains a
+// linux.FUSEInitOut with less attributes.
+//
+// Dynamically-sized objects cannot be marshalled.
+type fuseInitRes struct {
+	marshal.StubMarshallable
+
+	// initOut contains the response from the FUSE server.
+	initOut linux.FUSEInitOut
+
+	// initLen is the total length of bytes of the response.
+	initLen uint32
+}
+
+// UnmarshalBytes deserializes src to the initOut attribute in a fuseInitRes.
+func (r *fuseInitRes) UnmarshalBytes(src []byte) {
+	out := &r.initOut
+
+	// Introduced before FUSE kernel version 7.13.
+	out.Major = uint32(usermem.ByteOrder.Uint32(src[:4]))
+	src = src[4:]
+	out.Minor = uint32(usermem.ByteOrder.Uint32(src[:4]))
+	src = src[4:]
+	out.MaxReadahead = uint32(usermem.ByteOrder.Uint32(src[:4]))
+	src = src[4:]
+	out.Flags = uint32(usermem.ByteOrder.Uint32(src[:4]))
+	src = src[4:]
+	out.MaxBackground = uint16(usermem.ByteOrder.Uint16(src[:2]))
+	src = src[2:]
+	out.CongestionThreshold = uint16(usermem.ByteOrder.Uint16(src[:2]))
+	src = src[2:]
+	out.MaxWrite = uint32(usermem.ByteOrder.Uint32(src[:4]))
+	src = src[4:]
+
+	// Introduced in FUSE kernel version 7.23.
+	if len(src) >= 4 {
+		out.TimeGran = uint32(usermem.ByteOrder.Uint32(src[:4]))
+		src = src[4:]
+	}
+	// Introduced in FUSE kernel version 7.28.
+	if len(src) >= 2 {
+		out.MaxPages = uint16(usermem.ByteOrder.Uint16(src[:2]))
+		src = src[2:]
+	}
+	// Introduced in FUSE kernel version 7.31.
+	if len(src) >= 2 {
+		out.MapAlignment = uint16(usermem.ByteOrder.Uint16(src[:2]))
+		src = src[2:]
+	}
+}
+
+// SizeBytes is the size of the payload of the FUSE_INIT response.
+func (r *fuseInitRes) SizeBytes() int {
+	return int(r.initLen)
+}