Cleanup host UDS support

This change fixes several issues with the fsgofer host UDS support. Notably, it
adds support for SOCK_SEQPACKET and SOCK_DGRAM sockets [1]. It also fixes
unsafe use of unet.Socket, which could cause a panic if Socket.FD is called
when err != nil, and calls to Socket.FD with nothing to prevent the garbage
collector from destroying and closing the socket.

A set of tests is added to exercise host UDS access. This required extracting
most of the syscall test runner into a library that can be used by custom
tests.

Updates #235
Updates #1003

[1] N.B. SOCK_DGRAM sockets are likely not particularly useful, as a server can
only reply to a client that binds first. We don't allow bind, so these are
unlikely to be used.

PiperOrigin-RevId: 275558502

2 files changed, 245 insertions, 0 deletions

diff --git a/test/uds/BUILD b/test/uds/BUILD
new file mode 100644
index 000000000..a3843e699
--- /dev/null
+++ b/test/uds/BUILD
@@ -0,0 +1,17 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+package(
+    default_visibility = ["//:sandbox"],
+    licenses = ["notice"],
+)
+
+go_library(
+    name = "uds",
+    testonly = 1,
+    srcs = ["uds.go"],
+    importpath = "gvisor.dev/gvisor/test/uds",
+    deps = [
+        "//pkg/log",
+        "//pkg/unet",
+    ],
+)
diff --git a/test/uds/uds.go b/test/uds/uds.go
new file mode 100644
index 000000000..b714c61b0
--- /dev/null
+++ b/test/uds/uds.go
@@ -0,0 +1,228 @@
+// 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 uds contains helpers for testing external UDS functionality.
+package uds
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/unet"
+)
+
+// createEchoSocket creates a socket that echoes back anything received.
+//
+// Only works for stream, seqpacket sockets.
+func createEchoSocket(path string, protocol int) (cleanup func(), err error) {
+	fd, err := syscall.Socket(syscall.AF_UNIX, protocol, 0)
+	if err != nil {
+		return nil, fmt.Errorf("error creating echo(%d) socket: %v", protocol, err)
+	}
+
+	if err := syscall.Bind(fd, &syscall.SockaddrUnix{Name: path}); err != nil {
+		return nil, fmt.Errorf("error binding echo(%d) socket: %v", protocol, err)
+	}
+
+	if err := syscall.Listen(fd, 0); err != nil {
+		return nil, fmt.Errorf("error listening echo(%d) socket: %v", protocol, err)
+	}
+
+	server, err := unet.NewServerSocket(fd)
+	if err != nil {
+		return nil, fmt.Errorf("error creating echo(%d) unet socket: %v", protocol, err)
+	}
+
+	acceptAndEchoOne := func() error {
+		s, err := server.Accept()
+		if err != nil {
+			return fmt.Errorf("failed to accept: %v", err)
+		}
+		defer s.Close()
+
+		for {
+			buf := make([]byte, 512)
+			for {
+				n, err := s.Read(buf)
+				if err == io.EOF {
+					return nil
+				}
+				if err != nil {
+					return fmt.Errorf("failed to read: %d, %v", n, err)
+				}
+
+				n, err = s.Write(buf[:n])
+				if err != nil {
+					return fmt.Errorf("failed to write: %d, %v", n, err)
+				}
+			}
+		}
+	}
+
+	go func() {
+		for {
+			if err := acceptAndEchoOne(); err != nil {
+				log.Warningf("Failed to handle echo(%d) socket: %v", protocol, err)
+				return
+			}
+		}
+	}()
+
+	cleanup = func() {
+		if err := server.Close(); err != nil {
+			log.Warningf("Failed to close echo(%d) socket: %v", protocol, err)
+		}
+	}
+
+	return cleanup, nil
+}
+
+// createNonListeningSocket creates a socket that is bound but not listening.
+//
+// Only relevant for stream, seqpacket sockets.
+func createNonListeningSocket(path string, protocol int) (cleanup func(), err error) {
+	fd, err := syscall.Socket(syscall.AF_UNIX, protocol, 0)
+	if err != nil {
+		return nil, fmt.Errorf("error creating nonlistening(%d) socket: %v", protocol, err)
+	}
+
+	if err := syscall.Bind(fd, &syscall.SockaddrUnix{Name: path}); err != nil {
+		return nil, fmt.Errorf("error binding nonlistening(%d) socket: %v", protocol, err)
+	}
+
+	cleanup = func() {
+		if err := syscall.Close(fd); err != nil {
+			log.Warningf("Failed to close nonlistening(%d) socket: %v", protocol, err)
+		}
+	}
+
+	return cleanup, nil
+}
+
+// createNullSocket creates a socket that reads anything received.
+//
+// Only works for dgram sockets.
+func createNullSocket(path string, protocol int) (cleanup func(), err error) {
+	fd, err := syscall.Socket(syscall.AF_UNIX, protocol, 0)
+	if err != nil {
+		return nil, fmt.Errorf("error creating null(%d) socket: %v", protocol, err)
+	}
+
+	if err := syscall.Bind(fd, &syscall.SockaddrUnix{Name: path}); err != nil {
+		return nil, fmt.Errorf("error binding null(%d) socket: %v", protocol, err)
+	}
+
+	s, err := unet.NewSocket(fd)
+	if err != nil {
+		return nil, fmt.Errorf("error creating null(%d) unet socket: %v", protocol, err)
+	}
+
+	go func() {
+		buf := make([]byte, 512)
+		for {
+			n, err := s.Read(buf)
+			if err != nil {
+				log.Warningf("failed to read: %d, %v", n, err)
+				return
+			}
+		}
+	}()
+
+	cleanup = func() {
+		if err := s.Close(); err != nil {
+			log.Warningf("Failed to close null(%d) socket: %v", protocol, err)
+		}
+	}
+
+	return cleanup, nil
+}
+
+type socketCreator func(path string, proto int) (cleanup func(), err error)
+
+// CreateSocketTree creates a local tree of unix domain sockets for use in
+// testing:
+//  * /stream/echo
+//  * /stream/nonlistening
+//  * /seqpacket/echo
+//  * /seqpacket/nonlistening
+//  * /dgram/null
+func CreateSocketTree(baseDir string) (dir string, cleanup func(), err error) {
+	dir, err = ioutil.TempDir(baseDir, "sockets")
+	if err != nil {
+		return "", nil, fmt.Errorf("error creating temp dir: %v", err)
+	}
+
+	var protocols = []struct {
+		protocol int
+		name     string
+		sockets  map[string]socketCreator
+	}{
+		{
+			protocol: syscall.SOCK_STREAM,
+			name:     "stream",
+			sockets: map[string]socketCreator{
+				"echo":         createEchoSocket,
+				"nonlistening": createNonListeningSocket,
+			},
+		},
+		{
+			protocol: syscall.SOCK_SEQPACKET,
+			name:     "seqpacket",
+			sockets: map[string]socketCreator{
+				"echo":         createEchoSocket,
+				"nonlistening": createNonListeningSocket,
+			},
+		},
+		{
+			protocol: syscall.SOCK_DGRAM,
+			name:     "dgram",
+			sockets: map[string]socketCreator{
+				"null": createNullSocket,
+			},
+		},
+	}
+
+	var cleanups []func()
+	for _, proto := range protocols {
+		protoDir := filepath.Join(dir, proto.name)
+		if err := os.Mkdir(protoDir, 0755); err != nil {
+			return "", nil, fmt.Errorf("error creating %s dir: %v", proto.name, err)
+		}
+
+		for name, fn := range proto.sockets {
+			path := filepath.Join(protoDir, name)
+			cleanup, err := fn(path, proto.protocol)
+			if err != nil {
+				return "", nil, fmt.Errorf("error creating %s %s socket: %v", proto.name, name, err)
+			}
+
+			cleanups = append(cleanups, cleanup)
+		}
+	}
+
+	cleanup = func() {
+		for _, c := range cleanups {
+			c()
+		}
+
+		os.RemoveAll(dir)
+	}
+
+	return dir, cleanup, nil
+}