Always set SysProcAttr.Ctty to an FD in the child's FD table.

Go was going to change the behavior of SysProcAttr.Ctty such that it must be an
FD in the *parent* FD table:
https://go-review.googlesource.com/c/go/+/178919/

However, after some debate, it was decided that this change was too
backwards-incompatible, and so it was reverted.
https://github.com/golang/go/issues/29458

The behavior going forward is unchanged: the Ctty FD must be an FD in the
*child* FD table.

PiperOrigin-RevId: 255228476

5 files changed, 9 insertions, 70 deletions

diff --git a/runsc/cmd/exec.go b/runsc/cmd/exec.go
index 5a823e89a..e817eff77 100644
--- a/runsc/cmd/exec.go
+++ b/runsc/cmd/exec.go
@@ -235,18 +235,12 @@ func (ex *Exec) execChildAndWait(waitStatus *syscall.WaitStatus) subcommands.Exi
 		cmd.SysProcAttr = &syscall.SysProcAttr{
 			Setsid:  true,
 			Setctty: true,
-			Ctty:    int(tty.Fd()),
+			// The Ctty FD must be the FD in the child process's FD
+			// table. Since we set cmd.Stdin/Stdout/Stderr to the
+			// tty FD, we can use any of 0, 1, or 2 here.
+			// See https://github.com/golang/go/issues/29458.
+			Ctty: 0,
 		}
-		// TODO(b/133868570): Delete this check once Go 1.12 is no
-		// longer supported.
-		if console.CttyFdIsPostShuffle {
-			// In go1.12 and before, the Ctty FD must be the FD in
-			// the child process's FD table. Since we set
-			// cmd.Stdin/Stdout/Stderr to the tty FD, we can use
-			// any of 0, 1, or 2 here.
-			cmd.SysProcAttr.Ctty = 0
-		}
-
 	}
 
 	if err := cmd.Start(); err != nil {
diff --git a/runsc/console/BUILD b/runsc/console/BUILD
index b7d8f32ca..e623c1a0f 100644
--- a/runsc/console/BUILD
+++ b/runsc/console/BUILD
@@ -6,8 +6,6 @@ go_library(
     name = "console",
     srcs = [
         "console.go",
-        "ctty_1_12.go",
-        "ctty_1_13.go",
     ],
     importpath = "gvisor.dev/gvisor/runsc/console",
     visibility = [
diff --git a/runsc/console/ctty_1_12.go b/runsc/console/ctty_1_12.go
deleted file mode 100644
index 6e7a314a3..000000000
--- a/runsc/console/ctty_1_12.go
+++ /dev/null
@@ -1,24 +0,0 @@
-// 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.
-
-// +build go1.12
-// +build !go1.13
-
-// TODO(b/133868570): Delete once Go 1.12 is no longer supported.
-
-package console
-
-// CttyFdIsPostShuffle indicates that in go1.12 and earlier, the
-// SysProcAttr.Ctty FD is determined "pre-shuffle" (not "post-shuffle").
-var CttyFdIsPostShuffle = false
diff --git a/runsc/console/ctty_1_13.go b/runsc/console/ctty_1_13.go
deleted file mode 100644
index 785d720e1..000000000
--- a/runsc/console/ctty_1_13.go
+++ /dev/null
@@ -1,24 +0,0 @@
-// 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.
-
-// +build go1.13
-// +build !go1.14
-
-// TODO(b/133868570): Delete once Go 1.12 is no longer supported.
-
-package console
-
-// CttyFdIsPostShuffle indicates that in go1.13 and later, the SysProcAttr.Ctty
-// FD is determined "post-shuffle".
-var CttyFdIsPostShuffle = true
diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index 1591052cd..6bebf0737 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -438,15 +438,10 @@ func (s *Sandbox) createSandboxProcess(conf *boot.Config, args *Args, startSyncF
 
 		// Set the TTY as a controlling TTY on the sandbox process.
 		cmd.SysProcAttr.Setctty = true
-		cmd.SysProcAttr.Ctty = int(tty.Fd())
-		// TODO(b/133868570): Delete this check once Go 1.12 is no
-		// longer supported.
-		if console.CttyFdIsPostShuffle {
-			// In go1.12 and before, the Ctty FD must be the FD in
-			// the child process's FD table, which will be "nextFD"
-			// in this case.
-			cmd.SysProcAttr.Ctty = nextFD
-		}
+		// The Ctty FD must be the FD in the child process's FD table,
+		// which will be nextFD in this case.
+		// See https://github.com/golang/go/issues/29458.
+		cmd.SysProcAttr.Ctty = nextFD
 
 		// Pass the tty as all stdio fds to sandbox.
 		for i := 0; i < 3; i++ {