runsc: Terminal support for "docker exec -ti".

This CL adds terminal support for "docker exec".  We previously only supported
consoles for the container process, but not exec processes.

The SYS_IOCTL syscall was added to the default seccomp filter list, but only
for ioctls that get/set winsize and termios structs. We need to allow these
ioctl for all containers because it's possible to run "exec -ti" on a
container that was started without an attached console, after the filters
have been installed.

Note that control-character signals are still not properly supported.

Tested with:
	$ docker run --runtime=runsc -it alpine
In another terminial:
	$ docker exec -it <containerid> /bin/sh

PiperOrigin-RevId: 210185456
Change-Id: I6d2401e53a7697bb988c120a8961505c335f96d9

2 files changed, 77 insertions, 0 deletions

diff --git a/runsc/console/BUILD b/runsc/console/BUILD
new file mode 100644
index 000000000..fa1a7d430
--- /dev/null
+++ b/runsc/console/BUILD
@@ -0,0 +1,16 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "console",
+    srcs = ["console.go"],
+    importpath = "gvisor.googlesource.com/gvisor/runsc/console",
+    visibility = [
+        "//runsc:__subpackages__",
+    ],
+    deps = [
+        "@com_github_kr_pty//:go_default_library",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
diff --git a/runsc/console/console.go b/runsc/console/console.go
new file mode 100644
index 000000000..2f2745b2b
--- /dev/null
+++ b/runsc/console/console.go
@@ -0,0 +1,61 @@
+// 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 console contains utilities for working with pty consols in runsc.
+package console
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/kr/pty"
+	"golang.org/x/sys/unix"
+)
+
+// NewWithSocket creates pty master/slave pair, sends the master FD over the given
+// socket, and returns the slave.
+func NewWithSocket(socketPath string) (*os.File, error) {
+	// Create a new pty master and slave.
+	ptyMaster, ptySlave, err := pty.Open()
+	if err != nil {
+		return nil, fmt.Errorf("error opening pty: %v", err)
+	}
+	defer ptyMaster.Close()
+
+	// Get a connection to the socket path.
+	conn, err := net.Dial("unix", socketPath)
+	if err != nil {
+		ptySlave.Close()
+		return nil, fmt.Errorf("error dial socket %q: %v", socketPath, err)
+	}
+	uc, ok := conn.(*net.UnixConn)
+	if !ok {
+		ptySlave.Close()
+		return nil, fmt.Errorf("connection is not a UnixConn: %T", conn)
+	}
+	socket, err := uc.File()
+	if err != nil {
+		ptySlave.Close()
+		return nil, fmt.Errorf("error getting file for unix socket %v: %v", uc, err)
+	}
+
+	// Send the master FD over the connection.
+	msg := unix.UnixRights(int(ptyMaster.Fd()))
+	if err := unix.Sendmsg(int(socket.Fd()), []byte("pty-master"), msg, nil, 0); err != nil {
+		ptySlave.Close()
+		return nil, fmt.Errorf("error sending console over unix socket %q: %v", socketPath, err)
+	}
+	return ptySlave, nil
+}