runc run/exec: fix terminal wrt stdin redirection

kolyshkin · kolyshkin · commit b79cb04886d8 · 2020-08-20T07:56:20.000-07:00
This fixes the following failure: > sudo runc run -b bundle ctr </dev/null > WARN[0000] exit status 2 > ERRO[0000] container_linux.go:367: starting container process caused: process_linux.go:459: container init caused: The "exit status 2" with no error message is caused by SIGHUP which is sent to init by the kernel when we are losing the controlling terminal. If we choose to ignore that, we'll get panic in console.Current(), which is addressed by [1]. Otherwise, the issue here is simple: the code assumes stdin is opened to a terminal, and fails to work otherwise. Some standard Linux tools (e.g. stty, top) do the same (modulo panic), while some others (reset, tput) use the trick of trying all the three std streams (starting with stderr as it is least likely to be redirected), and if all three fails, open /dev/tty. This commit does a similar thing (see initHostConsole). It also replaces the call to console.Current(), which may panic (see [1]), by reusing the t.hostConsole. Finally, a simple test case is added. Fixes: opencontainers#2485 [1] containerd/console#37 Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
diff --git a/tty.go b/tty.go
@@ -12,16 +12,17 @@ import (
 	"github.com/containerd/console"
 	"github.com/opencontainers/runc/libcontainer"
 	"github.com/opencontainers/runc/libcontainer/utils"
+	"github.com/pkg/errors"
 )
 
 type tty struct {
-	epoller   *console.Epoller
-	console   *console.EpollConsole
-	stdin     console.Console
-	closers   []io.Closer
-	postStart []io.Closer
-	wg        sync.WaitGroup
-	consoleC  chan error
+	epoller     *console.Epoller
+	console     *console.EpollConsole
+	hostConsole console.Console
+	closers     []io.Closer
+	postStart   []io.Closer
+	wg          sync.WaitGroup
+	consoleC    chan error
 }
 
 func (t *tty) copyIO(w io.Writer, r io.ReadCloser) {
@@ -71,6 +72,37 @@ func inheritStdio(process *libcontainer.Process) error {
 	return nil
 }
 
+func (t *tty) initHostConsole() error {
+	// Usually all three (stdin, stdout, and stderr) streams are open to
+	// the terminal, but they might be redirected, so try them all.
+	for _, s := range []*os.File{os.Stderr, os.Stdout, os.Stdin} {
+		c, err := console.ConsoleFromFile(s)
+		switch err {
+		case nil:
+			t.hostConsole = c
+			return nil
+		case console.ErrNotAConsole:
+			continue
+		default:
+			// should not happen
+			return errors.Wrap(err, "unable to get console")
+		}
+	}
+	// If all streams are redirected, but we still have a controlling
+	// terminal, it can be obtained by opening /dev/tty.
+	tty, err := os.Open("/dev/tty")
+	if err != nil {
+		return err
+	}
+	c, err := console.ConsoleFromFile(tty)
+	if err != nil {
+		return errors.Wrap(err, "unable to get console")
+	}
+
+	t.hostConsole = c
+	return nil
+}
+
 func (t *tty) recvtty(process *libcontainer.Process, socket *os.File) (Err error) {
 	f, err := utils.RecvFd(socket)
 	if err != nil {
@@ -99,18 +131,13 @@ func (t *tty) recvtty(process *libcontainer.Process, socket *os.File) (Err error
 	t.wg.Add(1)
 	go t.copyIO(os.Stdout, epollConsole)
 
-	// set raw mode to stdin and also handle interrupt
-	stdin, err := console.ConsoleFromFile(os.Stdin)
-	if err != nil {
-		return err
-	}
-	if err := stdin.SetRaw(); err != nil {
+	// Set raw mode for the controlling terminal.
+	if err := t.hostConsole.SetRaw(); err != nil {
 		return fmt.Errorf("failed to set the terminal from the stdin: %v", err)
 	}
-	go handleInterrupt(stdin)
+	go handleInterrupt(t.hostConsole)
 
 	t.epoller = epoller
-	t.stdin = stdin
 	t.console = epollConsole
 	t.closers = []io.Closer{epollConsole}
 	return nil
@@ -156,15 +183,15 @@ func (t *tty) Close() error {
 	for _, c := range t.closers {
 		c.Close()
 	}
-	if t.stdin != nil {
-		t.stdin.Reset()
+	if t.hostConsole != nil {
+		t.hostConsole.Reset()
 	}
 	return nil
 }
 
 func (t *tty) resize() error {
-	if t.console == nil {
+	if t.console == nil || t.hostConsole == nil {
 		return nil
 	}
-	return t.console.ResizeFrom(console.Current())
+	return t.console.ResizeFrom(t.hostConsole)
 }
diff --git a/utils_linux.go b/utils_linux.go
@@ -157,6 +157,9 @@ func setupIO(process *libcontainer.Process, rootuid, rootgid int, createTTY, det
 		process.Stderr = nil
 		t := &tty{}
 		if !detach {
+			if err := t.initHostConsole(); err != nil {
+				return nil, err
+			}
 			parent, child, err := utils.NewSockPair("console")
 			if err != nil {
 				return nil, err
