Job control: controlling TTYs and foreground process groups.

(Don't worry, this is mostly tests.)

Implemented the following ioctls:
- TIOCSCTTY - set controlling TTY
- TIOCNOTTY - remove controlling tty, maybe signal some other processes
- TIOCGPGRP - get foreground process group. Also enables tcgetpgrp().
- TIOCSPGRP - set foreground process group. Also enabled tcsetpgrp().

Next steps are to actually turn terminal-generated control characters (e.g. C^c)
into signals to the proper process groups, and to send SIGTTOU and SIGTTIN when
appropriate.

PiperOrigin-RevId: 261387276

17 files changed, 851 insertions, 34 deletions

diff --git a/pkg/sentry/fs/tty/BUILD b/pkg/sentry/fs/tty/BUILD
index 5e9327aec..291164986 100644
--- a/pkg/sentry/fs/tty/BUILD
+++ b/pkg/sentry/fs/tty/BUILD
@@ -23,6 +23,7 @@ go_library(
         "//pkg/sentry/device",
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/fsutil",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/safemem",
         "//pkg/sentry/socket/unix/transport",
diff --git a/pkg/sentry/fs/tty/dir.go b/pkg/sentry/fs/tty/dir.go
index 1d128532b..2f639c823 100644
--- a/pkg/sentry/fs/tty/dir.go
+++ b/pkg/sentry/fs/tty/dir.go
@@ -129,6 +129,9 @@ func newDir(ctx context.Context, m *fs.MountSource) *fs.Inode {
 
 // Release implements fs.InodeOperations.Release.
 func (d *dirInodeOperations) Release(ctx context.Context) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
 	d.master.DecRef()
 	if len(d.slaves) != 0 {
 		panic(fmt.Sprintf("devpts directory still contains active terminals: %+v", d))
diff --git a/pkg/sentry/fs/tty/master.go b/pkg/sentry/fs/tty/master.go
index 92ec1ca18..19b7557d5 100644
--- a/pkg/sentry/fs/tty/master.go
+++ b/pkg/sentry/fs/tty/master.go
@@ -172,6 +172,19 @@ func (mf *masterFileOperations) Ioctl(ctx context.Context, _ *fs.File, io userme
 		return 0, mf.t.ld.windowSize(ctx, io, args)
 	case linux.TIOCSWINSZ:
 		return 0, mf.t.ld.setWindowSize(ctx, io, args)
+	case linux.TIOCSCTTY:
+		// Make the given terminal the controlling terminal of the
+		// calling process.
+		return 0, mf.t.setControllingTTY(ctx, io, args, true /* isMaster */)
+	case linux.TIOCNOTTY:
+		// Release this process's controlling terminal.
+		return 0, mf.t.releaseControllingTTY(ctx, io, args, true /* isMaster */)
+	case linux.TIOCGPGRP:
+		// Get the foreground process group.
+		return mf.t.foregroundProcessGroup(ctx, io, args, true /* isMaster */)
+	case linux.TIOCSPGRP:
+		// Set the foreground process group.
+		return mf.t.setForegroundProcessGroup(ctx, io, args, true /* isMaster */)
 	default:
 		maybeEmitUnimplementedEvent(ctx, cmd)
 		return 0, syserror.ENOTTY
@@ -185,8 +198,6 @@ func maybeEmitUnimplementedEvent(ctx context.Context, cmd uint32) {
 		linux.TCSETS,
 		linux.TCSETSW,
 		linux.TCSETSF,
-		linux.TIOCGPGRP,
-		linux.TIOCSPGRP,
 		linux.TIOCGWINSZ,
 		linux.TIOCSWINSZ,
 		linux.TIOCSETD,
@@ -200,8 +211,6 @@ func maybeEmitUnimplementedEvent(ctx context.Context, cmd uint32) {
 		linux.TIOCEXCL,
 		linux.TIOCNXCL,
 		linux.TIOCGEXCL,
-		linux.TIOCNOTTY,
-		linux.TIOCSCTTY,
 		linux.TIOCGSID,
 		linux.TIOCGETD,
 		linux.TIOCVHANGUP,
diff --git a/pkg/sentry/fs/tty/slave.go b/pkg/sentry/fs/tty/slave.go
index e30266404..944c4ada1 100644
--- a/pkg/sentry/fs/tty/slave.go
+++ b/pkg/sentry/fs/tty/slave.go
@@ -152,9 +152,16 @@ func (sf *slaveFileOperations) Ioctl(ctx context.Context, _ *fs.File, io usermem
 	case linux.TIOCSCTTY:
 		// Make the given terminal the controlling terminal of the
 		// calling process.
-		// TODO(b/129283598): Implement once we have support for job
-		// control.
-		return 0, nil
+		return 0, sf.si.t.setControllingTTY(ctx, io, args, false /* isMaster */)
+	case linux.TIOCNOTTY:
+		// Release this process's controlling terminal.
+		return 0, sf.si.t.releaseControllingTTY(ctx, io, args, false /* isMaster */)
+	case linux.TIOCGPGRP:
+		// Get the foreground process group.
+		return sf.si.t.foregroundProcessGroup(ctx, io, args, false /* isMaster */)
+	case linux.TIOCSPGRP:
+		// Set the foreground process group.
+		return sf.si.t.setForegroundProcessGroup(ctx, io, args, false /* isMaster */)
 	default:
 		maybeEmitUnimplementedEvent(ctx, cmd)
 		return 0, syserror.ENOTTY
diff --git a/pkg/sentry/fs/tty/terminal.go b/pkg/sentry/fs/tty/terminal.go
index b7cecb2ed..ff8138820 100644
--- a/pkg/sentry/fs/tty/terminal.go
+++ b/pkg/sentry/fs/tty/terminal.go
@@ -17,7 +17,10 @@ package tty
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
 )
 
 // Terminal is a pseudoterminal.
@@ -26,23 +29,100 @@ import (
 type Terminal struct {
 	refs.AtomicRefCount
 
-	// n is the terminal index.
+	// n is the terminal index. It is immutable.
 	n uint32
 
-	// d is the containing directory.
+	// d is the containing directory. It is immutable.
 	d *dirInodeOperations
 
-	// ld is the line discipline of the terminal.
+	// ld is the line discipline of the terminal. It is immutable.
 	ld *lineDiscipline
+
+	// masterKTTY contains the controlling process of the master end of
+	// this terminal. This field is immutable.
+	masterKTTY *kernel.TTY
+
+	// slaveKTTY contains the controlling process of the slave end of this
+	// terminal. This field is immutable.
+	slaveKTTY *kernel.TTY
 }
 
 func newTerminal(ctx context.Context, d *dirInodeOperations, n uint32) *Terminal {
 	termios := linux.DefaultSlaveTermios
 	t := Terminal{
-		d:  d,
-		n:  n,
-		ld: newLineDiscipline(termios),
+		d:          d,
+		n:          n,
+		ld:         newLineDiscipline(termios),
+		masterKTTY: &kernel.TTY{},
+		slaveKTTY:  &kernel.TTY{},
 	}
 	t.EnableLeakCheck("tty.Terminal")
 	return &t
 }
+
+// setControllingTTY makes tm the controlling terminal of the calling thread
+// group.
+func (tm *Terminal) setControllingTTY(ctx context.Context, io usermem.IO, args arch.SyscallArguments, isMaster bool) error {
+	task := kernel.TaskFromContext(ctx)
+	if task == nil {
+		panic("setControllingTTY must be called from a task context")
+	}
+
+	return task.ThreadGroup().SetControllingTTY(tm.tty(isMaster), args[2].Int())
+}
+
+// releaseControllingTTY removes tm as the controlling terminal of the calling
+// thread group.
+func (tm *Terminal) releaseControllingTTY(ctx context.Context, io usermem.IO, args arch.SyscallArguments, isMaster bool) error {
+	task := kernel.TaskFromContext(ctx)
+	if task == nil {
+		panic("releaseControllingTTY must be called from a task context")
+	}
+
+	return task.ThreadGroup().ReleaseControllingTTY(tm.tty(isMaster))
+}
+
+// foregroundProcessGroup gets the process group ID of tm's foreground process.
+func (tm *Terminal) foregroundProcessGroup(ctx context.Context, io usermem.IO, args arch.SyscallArguments, isMaster bool) (uintptr, error) {
+	task := kernel.TaskFromContext(ctx)
+	if task == nil {
+		panic("foregroundProcessGroup must be called from a task context")
+	}
+
+	ret, err := task.ThreadGroup().ForegroundProcessGroup(tm.tty(isMaster))
+	if err != nil {
+		return 0, err
+	}
+
+	// Write it out to *arg.
+	_, err = usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(ret), usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	return 0, err
+}
+
+// foregroundProcessGroup sets tm's foreground process.
+func (tm *Terminal) setForegroundProcessGroup(ctx context.Context, io usermem.IO, args arch.SyscallArguments, isMaster bool) (uintptr, error) {
+	task := kernel.TaskFromContext(ctx)
+	if task == nil {
+		panic("setForegroundProcessGroup must be called from a task context")
+	}
+
+	// Read in the process group ID.
+	var pgid int32
+	if _, err := usermem.CopyObjectIn(ctx, io, args[2].Pointer(), &pgid, usermem.IOOpts{
+		AddressSpaceActive: true,
+	}); err != nil {
+		return 0, err
+	}
+
+	ret, err := task.ThreadGroup().SetForegroundProcessGroup(tm.tty(isMaster), kernel.ProcessGroupID(pgid))
+	return uintptr(ret), err
+}
+
+func (tm *Terminal) tty(isMaster bool) *kernel.TTY {
+	if isMaster {
+		return tm.masterKTTY
+	}
+	return tm.slaveKTTY
+}
diff --git a/pkg/sentry/kernel/BUILD b/pkg/sentry/kernel/BUILD
index e61d39c82..41bee9a22 100644
--- a/pkg/sentry/kernel/BUILD
+++ b/pkg/sentry/kernel/BUILD
@@ -144,6 +144,7 @@ go_library(
         "threads.go",
         "timekeeper.go",
         "timekeeper_state.go",
+        "tty.go",
         "uts_namespace.go",
         "vdso.go",
         "version.go",
diff --git a/pkg/sentry/kernel/sessions.go b/pkg/sentry/kernel/sessions.go
index 81fcd8258..e5f297478 100644
--- a/pkg/sentry/kernel/sessions.go
+++ b/pkg/sentry/kernel/sessions.go
@@ -47,6 +47,11 @@ type Session struct {
 	// The id is immutable.
 	id SessionID
 
+	// foreground is the foreground process group.
+	//
+	// This is protected by TaskSet.mu.
+	foreground *ProcessGroup
+
 	// ProcessGroups is a list of process groups in this Session. This is
 	// protected by TaskSet.mu.
 	processGroups processGroupList
@@ -260,12 +265,14 @@ func (pg *ProcessGroup) SendSignal(info *arch.SignalInfo) error {
 func (tg *ThreadGroup) CreateSession() error {
 	tg.pidns.owner.mu.Lock()
 	defer tg.pidns.owner.mu.Unlock()
+	tg.signalHandlers.mu.Lock()
+	defer tg.signalHandlers.mu.Unlock()
 	return tg.createSession()
 }
 
 // createSession creates a new session for a threadgroup.
 //
-// Precondition: callers must hold TaskSet.mu for writing.
+// Precondition: callers must hold TaskSet.mu and the signal mutex for writing.
 func (tg *ThreadGroup) createSession() error {
 	// Get the ID for this thread in the current namespace.
 	id := tg.pidns.tgids[tg]
@@ -346,6 +353,9 @@ func (tg *ThreadGroup) createSession() error {
 		ns.processGroups[ProcessGroupID(local)] = pg
 	}
 
+	// Disconnect from the controlling terminal.
+	tg.tty = nil
+
 	return nil
 }
 
diff --git a/pkg/sentry/kernel/task_start.go b/pkg/sentry/kernel/task_start.go
index d60cd62c7..ae6fc4025 100644
--- a/pkg/sentry/kernel/task_start.go
+++ b/pkg/sentry/kernel/task_start.go
@@ -172,9 +172,10 @@ func (ts *TaskSet) newTask(cfg *TaskConfig) (*Task, error) {
 		if parentPG := tg.parentPG(); parentPG == nil {
 			tg.createSession()
 		} else {
-			// Inherit the process group.
+			// Inherit the process group and terminal.
 			parentPG.incRefWithParent(parentPG)
 			tg.processGroup = parentPG
+			tg.tty = t.parent.tg.tty
 		}
 	}
 	tg.tasks.PushBack(t)
diff --git a/pkg/sentry/kernel/thread_group.go b/pkg/sentry/kernel/thread_group.go
index 2a97e3e8e..0eef24bfb 100644
--- a/pkg/sentry/kernel/thread_group.go
+++ b/pkg/sentry/kernel/thread_group.go
@@ -19,10 +19,13 @@ import (
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
 	"gvisor.dev/gvisor/pkg/sentry/limits"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // A ThreadGroup is a logical grouping of tasks that has widespread
@@ -245,6 +248,12 @@ type ThreadGroup struct {
 	//
 	// mounts is immutable.
 	mounts *fs.MountNamespace
+
+	// tty is the thread group's controlling terminal. If nil, there is no
+	// controlling terminal.
+	//
+	// tty is protected by the signal mutex.
+	tty *TTY
 }
 
 // newThreadGroup returns a new, empty thread group in PID namespace ns. The
@@ -324,6 +333,176 @@ func (tg *ThreadGroup) forEachChildThreadGroupLocked(fn func(*ThreadGroup)) {
 	}
 }
 
+// SetControllingTTY sets tty as the controlling terminal of tg.
+func (tg *ThreadGroup) SetControllingTTY(tty *TTY, arg int32) error {
+	tty.mu.Lock()
+	defer tty.mu.Unlock()
+
+	// We might be asked to set the controlling terminal of multiple
+	// processes, so we lock both the TaskSet and SignalHandlers.
+	tg.pidns.owner.mu.Lock()
+	defer tg.pidns.owner.mu.Unlock()
+	tg.signalHandlers.mu.Lock()
+	defer tg.signalHandlers.mu.Unlock()
+
+	// "The calling process must be a session leader and not have a
+	// controlling terminal already." - tty_ioctl(4)
+	if tg.processGroup.session.leader != tg || tg.tty != nil {
+		return syserror.EINVAL
+	}
+
+	// "If this terminal is already the controlling terminal of a different
+	// session group, then the ioctl fails with EPERM, unless the caller
+	// has the CAP_SYS_ADMIN capability and arg equals 1, in which case the
+	// terminal is stolen, and all processes that had it as controlling
+	// terminal lose it." - tty_ioctl(4)
+	if tty.tg != nil && tg.processGroup.session != tty.tg.processGroup.session {
+		if !auth.CredentialsFromContext(tg.leader).HasCapability(linux.CAP_SYS_ADMIN) || arg != 1 {
+			return syserror.EPERM
+		}
+		// Steal the TTY away. Unlike TIOCNOTTY, don't send signals.
+		for othertg := range tg.pidns.owner.Root.tgids {
+			// This won't deadlock by locking tg.signalHandlers
+			// because at this point:
+			// - We only lock signalHandlers if it's in the same
+			//   session as the tty's controlling thread group.
+			// - We know that the calling thread group is not in
+			//   the same session as the tty's controlling thread
+			//   group.
+			if othertg.processGroup.session == tty.tg.processGroup.session {
+				othertg.signalHandlers.mu.Lock()
+				othertg.tty = nil
+				othertg.signalHandlers.mu.Unlock()
+			}
+		}
+	}
+
+	// Set the controlling terminal and foreground process group.
+	tg.tty = tty
+	tg.processGroup.session.foreground = tg.processGroup
+	// Set this as the controlling process of the terminal.
+	tty.tg = tg
+
+	return nil
+}
+
+// ReleaseControllingTTY gives up tty as the controlling tty of tg.
+func (tg *ThreadGroup) ReleaseControllingTTY(tty *TTY) error {
+	tty.mu.Lock()
+	defer tty.mu.Unlock()
+
+	// We might be asked to set the controlling terminal of multiple
+	// processes, so we lock both the TaskSet and SignalHandlers.
+	tg.pidns.owner.mu.RLock()
+	defer tg.pidns.owner.mu.RUnlock()
+
+	// Just below, we may re-lock signalHandlers in order to send signals.
+	// Thus we can't defer Unlock here.
+	tg.signalHandlers.mu.Lock()
+
+	if tg.tty == nil || tg.tty != tty {
+		tg.signalHandlers.mu.Unlock()
+		return syserror.ENOTTY
+	}
+
+	// "If the process was session leader, then send SIGHUP and SIGCONT to
+	// the foreground process group and all processes in the current
+	// session lose their controlling terminal." - tty_ioctl(4)
+	// Remove tty as the controlling tty for each process in the session,
+	// then send them SIGHUP and SIGCONT.
+
+	// If we're not the session leader, we don't have to do much.
+	if tty.tg != tg {
+		tg.tty = nil
+		tg.signalHandlers.mu.Unlock()
+		return nil
+	}
+
+	tg.signalHandlers.mu.Unlock()
+
+	// We're the session leader. SIGHUP and SIGCONT the foreground process
+	// group and remove all controlling terminals in the session.
+	var lastErr error
+	for othertg := range tg.pidns.owner.Root.tgids {
+		if othertg.processGroup.session == tg.processGroup.session {
+			othertg.signalHandlers.mu.Lock()
+			othertg.tty = nil
+			if othertg.processGroup == tg.processGroup.session.foreground {
+				if err := othertg.leader.sendSignalLocked(&arch.SignalInfo{Signo: int32(linux.SIGHUP)}, true /* group */); err != nil {
+					lastErr = err
+				}
+				if err := othertg.leader.sendSignalLocked(&arch.SignalInfo{Signo: int32(linux.SIGCONT)}, true /* group */); err != nil {
+					lastErr = err
+				}
+			}
+			othertg.signalHandlers.mu.Unlock()
+		}
+	}
+
+	return lastErr
+}
+
+// ForegroundProcessGroup returns the process group ID of the foreground
+// process group.
+func (tg *ThreadGroup) ForegroundProcessGroup(tty *TTY) (int32, error) {
+	tty.mu.Lock()
+	defer tty.mu.Unlock()
+
+	tg.pidns.owner.mu.Lock()
+	defer tg.pidns.owner.mu.Unlock()
+	tg.signalHandlers.mu.Lock()
+	defer tg.signalHandlers.mu.Unlock()
+
+	// "When fd does not refer to the controlling terminal of the calling
+	// process, -1 is returned" - tcgetpgrp(3)
+	if tg.tty != tty {
+		return -1, syserror.ENOTTY
+	}
+
+	return int32(tg.processGroup.session.foreground.id), nil
+}
+
+// SetForegroundProcessGroup sets the foreground process group of tty to pgid.
+func (tg *ThreadGroup) SetForegroundProcessGroup(tty *TTY, pgid ProcessGroupID) (int32, error) {
+	tty.mu.Lock()
+	defer tty.mu.Unlock()
+
+	tg.pidns.owner.mu.Lock()
+	defer tg.pidns.owner.mu.Unlock()
+	tg.signalHandlers.mu.Lock()
+	defer tg.signalHandlers.mu.Unlock()
+
+	// TODO(b/129283598): "If tcsetpgrp() is called by a member of a
+	// background process group in its session, and the calling process is
+	// not blocking or ignoring SIGTTOU, a SIGTTOU signal is sent to all
+	// members of this background process group."
+
+	// tty must be the controlling terminal.
+	if tg.tty != tty {
+		return -1, syserror.ENOTTY
+	}
+
+	// pgid must be positive.
+	if pgid < 0 {
+		return -1, syserror.EINVAL
+	}
+
+	// pg must not be empty. Empty process groups are removed from their
+	// pid namespaces.
+	pg, ok := tg.pidns.processGroups[pgid]
+	if !ok {
+		return -1, syserror.ESRCH
+	}
+
+	// pg must be part of this process's session.
+	if tg.processGroup.session != pg.session {
+		return -1, syserror.EPERM
+	}
+
+	tg.processGroup.session.foreground.id = pgid
+	return 0, nil
+}
+
 // itimerRealListener implements ktime.Listener for ITIMER_REAL expirations.
 //
 // +stateify savable
diff --git a/pkg/sentry/kernel/tty.go b/pkg/sentry/kernel/tty.go
new file mode 100644
index 000000000..34f84487a
--- /dev/null
+++ b/pkg/sentry/kernel/tty.go
@@ -0,0 +1,28 @@
+// Copyright 2018 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 kernel
+
+import "sync"
+
+// TTY defines the relationship between a thread group and its controlling
+// terminal.
+//
+// +stateify savable
+type TTY struct {
+	mu sync.Mutex `state:"nosave"`
+
+	// tg is protected by mu.
+	tg *ThreadGroup
+}
diff --git a/test/syscalls/BUILD b/test/syscalls/BUILD
index 841a0f2e1..a3e43cad2 100644
--- a/test/syscalls/BUILD
+++ b/test/syscalls/BUILD
@@ -310,6 +310,10 @@ syscall_test(
 )
 
 syscall_test(
+    test = "//test/syscalls/linux:pty_root_test",
+)
+
+syscall_test(
     add_overlay = True,
     test = "//test/syscalls/linux:pwritev2_test",
 )
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 40fc73812..16666e772 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -1214,8 +1214,10 @@ cc_binary(
     srcs = ["pty.cc"],
     linkstatic = 1,
     deps = [
+        "//test/util:capability_util",
         "//test/util:file_descriptor",
         "//test/util:posix_error",
+        "//test/util:pty_util",
         "//test/util:test_main",
         "//test/util:test_util",
         "//test/util:thread_util",
@@ -1228,6 +1230,23 @@ cc_binary(
 )
 
 cc_binary(
+    name = "pty_root_test",
+    testonly = 1,
+    srcs = ["pty_root.cc"],
+    linkstatic = 1,
+    deps = [
+        "//test/util:capability_util",
+        "//test/util:file_descriptor",
+        "//test/util:posix_error",
+        "//test/util:pty_util",
+        "//test/util:test_main",
+        "//test/util:thread_util",
+        "@com_google_absl//absl/base:core_headers",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_binary(
     name = "partial_bad_buffer_test",
     testonly = 1,
     srcs = ["partial_bad_buffer.cc"],
diff --git a/test/syscalls/linux/pty.cc b/test/syscalls/linux/pty.cc
index d1ab4703f..bd6907876 100644
--- a/test/syscalls/linux/pty.cc
+++ b/test/syscalls/linux/pty.cc
@@ -13,13 +13,17 @@
 // limitations under the License.
 
 #include <fcntl.h>
+#include <linux/capability.h>
 #include <linux/major.h>
 #include <poll.h>
+#include <sched.h>
+#include <signal.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
 #include <sys/types.h>
+#include <sys/wait.h>
 #include <termios.h>
 #include <unistd.h>
 
@@ -31,8 +35,10 @@
 #include "absl/synchronization/notification.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "test/util/capability_util.h"
 #include "test/util/file_descriptor.h"
 #include "test/util/posix_error.h"
+#include "test/util/pty_util.h"
 #include "test/util/test_util.h"
 #include "test/util/thread_util.h"
 
@@ -370,25 +376,6 @@ PosixErrorOr<size_t> PollAndReadFd(int fd, void* buf, size_t count,
   return PosixError(ETIMEDOUT, "Poll timed out");
 }
 
-// Opens the slave end of the passed master as R/W and nonblocking.
-PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master) {
-  // Get pty index.
-  int n;
-  int ret = ioctl(master.get(), TIOCGPTN, &n);
-  if (ret < 0) {
-    return PosixError(errno, "ioctl(TIOCGPTN) failed");
-  }
-
-  // Unlock pts.
-  int unlock = 0;
-  ret = ioctl(master.get(), TIOCSPTLCK, &unlock);
-  if (ret < 0) {
-    return PosixError(errno, "ioctl(TIOSPTLCK) failed");
-  }
-
-  return Open(absl::StrCat("/dev/pts/", n), O_RDWR | O_NONBLOCK);
-}
-
 TEST(BasicPtyTest, StatUnopenedMaster) {
   struct stat s;
   ASSERT_THAT(stat("/dev/ptmx", &s), SyscallSucceeds());
@@ -1233,6 +1220,340 @@ TEST_F(PtyTest, SetMasterWindowSize) {
   EXPECT_EQ(retrieved_ws.ws_col, kCols);
 }
 
+class JobControlTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    master_ = ASSERT_NO_ERRNO_AND_VALUE(Open("/dev/ptmx", O_RDWR | O_NONBLOCK));
+    slave_ = ASSERT_NO_ERRNO_AND_VALUE(OpenSlave(master_));
+
+    // Make this a session leader, which also drops the controlling terminal.
+    // In the gVisor test environment, this test will be run as the session
+    // leader already (as the sentry init process).
+    if (!IsRunningOnGvisor()) {
+      ASSERT_THAT(setsid(), SyscallSucceeds());
+    }
+  }
+
+  // Master and slave ends of the PTY. Non-blocking.
+  FileDescriptor master_;
+  FileDescriptor slave_;
+};
+
+TEST_F(JobControlTest, SetTTYMaster) {
+  ASSERT_THAT(ioctl(master_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, SetTTY) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, SetTTYNonLeader) {
+  // Fork a process that won't be the session leader.
+  pid_t child = fork();
+  if (!child) {
+    // We shouldn't be able to set the terminal.
+    TEST_PCHECK(ioctl(slave_.get(), TIOCSCTTY, 0));
+    _exit(0);
+  }
+
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_EQ(wstatus, 0);
+}
+
+TEST_F(JobControlTest, SetTTYBadArg) {
+  // Despite the man page saying arg should be 0 here, Linux doesn't actually
+  // check.
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 1), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, SetTTYDifferentSession) {
+  SKIP_IF(ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
+
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Fork, join a new session, and try to steal the parent's controlling
+  // terminal, which should fail.
+  pid_t child = fork();
+  if (!child) {
+    TEST_PCHECK(setsid() >= 0);
+    // We shouldn't be able to steal the terminal.
+    TEST_PCHECK(ioctl(slave_.get(), TIOCSCTTY, 1));
+    _exit(0);
+  }
+
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_EQ(wstatus, 0);
+}
+
+TEST_F(JobControlTest, ReleaseTTY) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Make sure we're ignoring SIGHUP, which will be sent to this process once we
+  // disconnect they TTY.
+  struct sigaction sa = {
+      .sa_handler = SIG_IGN,
+      .sa_flags = 0,
+  };
+  sigemptyset(&sa.sa_mask);
+  struct sigaction old_sa;
+  EXPECT_THAT(sigaction(SIGHUP, &sa, &old_sa), SyscallSucceeds());
+  EXPECT_THAT(ioctl(slave_.get(), TIOCNOTTY), SyscallSucceeds());
+  EXPECT_THAT(sigaction(SIGHUP, &old_sa, NULL), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, ReleaseUnsetTTY) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCNOTTY), SyscallFailsWithErrno(ENOTTY));
+}
+
+TEST_F(JobControlTest, ReleaseWrongTTY) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  ASSERT_THAT(ioctl(master_.get(), TIOCNOTTY), SyscallFailsWithErrno(ENOTTY));
+}
+
+TEST_F(JobControlTest, ReleaseTTYNonLeader) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  pid_t child = fork();
+  if (!child) {
+    TEST_PCHECK(!ioctl(slave_.get(), TIOCNOTTY));
+    _exit(0);
+  }
+
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_EQ(wstatus, 0);
+}
+
+TEST_F(JobControlTest, ReleaseTTYDifferentSession) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  pid_t child = fork();
+  if (!child) {
+    // Join a new session, then try to disconnect.
+    TEST_PCHECK(setsid() >= 0);
+    TEST_PCHECK(ioctl(slave_.get(), TIOCNOTTY));
+    _exit(0);
+  }
+
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_EQ(wstatus, 0);
+}
+
+// Used by the child process spawned in ReleaseTTYSignals to track received
+// signals.
+static int received;
+
+void sig_handler(int signum) { received |= signum; }
+
+// When the session leader releases its controlling terminal, the foreground
+// process group gets SIGHUP, then SIGCONT. This test:
+// - Spawns 2 threads
+// - Has thread 1 return 0 if it gets both SIGHUP and SIGCONT
+// - Has thread 2 leave the foreground process group, and return non-zero if it
+//   receives any signals.
+// - Has the parent thread release its controlling terminal
+// - Checks that thread 1 got both signals
+// - Checks that thread 2 didn't get any signals.
+TEST_F(JobControlTest, ReleaseTTYSignals) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  received = 0;
+  struct sigaction sa = {
+      .sa_handler = sig_handler,
+      .sa_flags = 0,
+  };
+  sigemptyset(&sa.sa_mask);
+  sigaddset(&sa.sa_mask, SIGHUP);
+  sigaddset(&sa.sa_mask, SIGCONT);
+  sigprocmask(SIG_BLOCK, &sa.sa_mask, NULL);
+
+  pid_t same_pgrp_child = fork();
+  if (!same_pgrp_child) {
+    // The child will wait for SIGHUP and SIGCONT, then return 0. It begins with
+    // SIGHUP and SIGCONT blocked. We install signal handlers for those signals,
+    // then use sigsuspend to wait for those specific signals.
+    TEST_PCHECK(!sigaction(SIGHUP, &sa, NULL));
+    TEST_PCHECK(!sigaction(SIGCONT, &sa, NULL));
+    sigset_t mask;
+    sigfillset(&mask);
+    sigdelset(&mask, SIGHUP);
+    sigdelset(&mask, SIGCONT);
+    while (received != (SIGHUP | SIGCONT)) {
+      sigsuspend(&mask);
+    }
+    _exit(0);
+  }
+
+  // We don't want to block these anymore.
+  sigprocmask(SIG_UNBLOCK, &sa.sa_mask, NULL);
+
+  // This child will return non-zero if either SIGHUP or SIGCONT are received.
+  pid_t diff_pgrp_child = fork();
+  if (!diff_pgrp_child) {
+    TEST_PCHECK(!setpgid(0, 0));
+    TEST_PCHECK(pause());
+    _exit(1);
+  }
+
+  EXPECT_THAT(setpgid(diff_pgrp_child, diff_pgrp_child), SyscallSucceeds());
+
+  // Make sure we're ignoring SIGHUP, which will be sent to this process once we
+  // disconnect they TTY.
+  struct sigaction sighup_sa = {
+      .sa_handler = SIG_IGN,
+      .sa_flags = 0,
+  };
+  sigemptyset(&sighup_sa.sa_mask);
+  struct sigaction old_sa;
+  EXPECT_THAT(sigaction(SIGHUP, &sighup_sa, &old_sa), SyscallSucceeds());
+
+  // Release the controlling terminal, sending SIGHUP and SIGCONT to all other
+  // processes in this process group.
+  EXPECT_THAT(ioctl(slave_.get(), TIOCNOTTY), SyscallSucceeds());
+
+  EXPECT_THAT(sigaction(SIGHUP, &old_sa, NULL), SyscallSucceeds());
+
+  // The child in the same process group will get signaled.
+  int wstatus;
+  EXPECT_THAT(waitpid(same_pgrp_child, &wstatus, 0),
+              SyscallSucceedsWithValue(same_pgrp_child));
+  EXPECT_EQ(wstatus, 0);
+
+  // The other child will not get signaled.
+  EXPECT_THAT(waitpid(diff_pgrp_child, &wstatus, WNOHANG),
+              SyscallSucceedsWithValue(0));
+  EXPECT_THAT(kill(diff_pgrp_child, SIGKILL), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, GetForegroundProcessGroup) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+  pid_t foreground_pgid;
+  pid_t pid;
+  ASSERT_THAT(ioctl(slave_.get(), TIOCGPGRP, &foreground_pgid),
+              SyscallSucceeds());
+  ASSERT_THAT(pid = getpid(), SyscallSucceeds());
+
+  ASSERT_EQ(foreground_pgid, pid);
+}
+
+TEST_F(JobControlTest, GetForegroundProcessGroupNonControlling) {
+  // At this point there's no controlling terminal, so TIOCGPGRP should fail.
+  pid_t foreground_pgid;
+  ASSERT_THAT(ioctl(slave_.get(), TIOCGPGRP, &foreground_pgid),
+              SyscallFailsWithErrno(ENOTTY));
+}
+
+// This test:
+// - sets itself as the foreground process group
+// - creates a child process in a new process group
+// - sets that child as the foreground process group
+// - kills its child and sets itself as the foreground process group.
+TEST_F(JobControlTest, SetForegroundProcessGroup) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Ignore SIGTTOU so that we don't stop ourself when calling tcsetpgrp.
+  struct sigaction sa = {
+      .sa_handler = SIG_IGN,
+      .sa_flags = 0,
+  };
+  sigemptyset(&sa.sa_mask);
+  sigaction(SIGTTOU, &sa, NULL);
+
+  // Set ourself as the foreground process group.
+  ASSERT_THAT(tcsetpgrp(slave_.get(), getpgid(0)), SyscallSucceeds());
+
+  // Create a new process that just waits to be signaled.
+  pid_t child = fork();
+  if (!child) {
+    TEST_PCHECK(!pause());
+    // We should never reach this.
+    _exit(1);
+  }
+
+  // Make the child its own process group, then make it the controlling process
+  // group of the terminal.
+  ASSERT_THAT(setpgid(child, child), SyscallSucceeds());
+  ASSERT_THAT(tcsetpgrp(slave_.get(), child), SyscallSucceeds());
+
+  // Sanity check - we're still the controlling session.
+  ASSERT_EQ(getsid(0), getsid(child));
+
+  // Signal the child, wait for it to exit, then retake the terminal.
+  ASSERT_THAT(kill(child, SIGTERM), SyscallSucceeds());
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_TRUE(WIFSIGNALED(wstatus));
+  ASSERT_EQ(WTERMSIG(wstatus), SIGTERM);
+
+  // Set ourself as the foreground process.
+  pid_t pgid;
+  ASSERT_THAT(pgid = getpgid(0), SyscallSucceeds());
+  ASSERT_THAT(tcsetpgrp(slave_.get(), pgid), SyscallSucceeds());
+}
+
+TEST_F(JobControlTest, SetForegroundProcessGroupWrongTTY) {
+  pid_t pid = getpid();
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSPGRP, &pid),
+              SyscallFailsWithErrno(ENOTTY));
+}
+
+TEST_F(JobControlTest, SetForegroundProcessGroupNegPgid) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  pid_t pid = -1;
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSPGRP, &pid),
+              SyscallFailsWithErrno(EINVAL));
+}
+
+TEST_F(JobControlTest, SetForegroundProcessGroupEmptyProcessGroup) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Create a new process, put it in a new process group, make that group the
+  // foreground process group, then have the process wait.
+  pid_t child = fork();
+  if (!child) {
+    TEST_PCHECK(!setpgid(0, 0));
+    _exit(0);
+  }
+
+  // Wait for the child to exit.
+  int wstatus;
+  EXPECT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  // The child's process group doesn't exist anymore - this should fail.
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSPGRP, &child),
+              SyscallFailsWithErrno(ESRCH));
+}
+
+TEST_F(JobControlTest, SetForegroundProcessGroupDifferentSession) {
+  ASSERT_THAT(ioctl(slave_.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Create a new process and put it in a new session.
+  pid_t child = fork();
+  if (!child) {
+    TEST_PCHECK(setsid() >= 0);
+    // Tell the parent we're in a new session.
+    TEST_PCHECK(!raise(SIGSTOP));
+    TEST_PCHECK(!pause());
+    _exit(1);
+  }
+
+  // Wait for the child to tell us it's in a new session.
+  int wstatus;
+  EXPECT_THAT(waitpid(child, &wstatus, WUNTRACED),
+              SyscallSucceedsWithValue(child));
+  EXPECT_TRUE(WSTOPSIG(wstatus));
+
+  // Child is in a new session, so we can't make it the foregroup process group.
+  EXPECT_THAT(ioctl(slave_.get(), TIOCSPGRP, &child),
+              SyscallFailsWithErrno(EPERM));
+
+  EXPECT_THAT(kill(child, SIGKILL), SyscallSucceeds());
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace gvisor
diff --git a/test/syscalls/linux/pty_root.cc b/test/syscalls/linux/pty_root.cc
new file mode 100644
index 000000000..14a4af980
--- /dev/null
+++ b/test/syscalls/linux/pty_root.cc
@@ -0,0 +1,68 @@
+// Copyright 2018 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.
+
+#include <sys/ioctl.h>
+#include <termios.h>
+
+#include "gtest/gtest.h"
+#include "absl/base/macros.h"
+#include "test/util/capability_util.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/posix_error.h"
+#include "test/util/pty_util.h"
+
+namespace gvisor {
+namespace testing {
+
+// These tests should be run as root.
+namespace {
+
+TEST(JobControlRootTest, StealTTY) {
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
+
+  // Make this a session leader, which also drops the controlling terminal.
+  // In the gVisor test environment, this test will be run as the session
+  // leader already (as the sentry init process).
+  if (!IsRunningOnGvisor()) {
+    ASSERT_THAT(setsid(), SyscallSucceeds());
+  }
+
+  FileDescriptor master =
+      ASSERT_NO_ERRNO_AND_VALUE(Open("/dev/ptmx", O_RDWR | O_NONBLOCK));
+  FileDescriptor slave = ASSERT_NO_ERRNO_AND_VALUE(OpenSlave(master));
+
+  // Make slave the controlling terminal.
+  ASSERT_THAT(ioctl(slave.get(), TIOCSCTTY, 0), SyscallSucceeds());
+
+  // Fork, join a new session, and try to steal the parent's controlling
+  // terminal, which should succeed when we have CAP_SYS_ADMIN and pass an arg
+  // of 1.
+  pid_t child = fork();
+  if (!child) {
+    ASSERT_THAT(setsid(), SyscallSucceeds());
+    // We shouldn't be able to steal the terminal with the wrong arg value.
+    TEST_PCHECK(ioctl(slave.get(), TIOCSCTTY, 0));
+    // We should be able to steal it here.
+    TEST_PCHECK(!ioctl(slave.get(), TIOCSCTTY, 1));
+    _exit(0);
+  }
+
+  int wstatus;
+  ASSERT_THAT(waitpid(child, &wstatus, 0), SyscallSucceedsWithValue(child));
+  ASSERT_EQ(wstatus, 0);
+}
+
+}  // namespace
+}  // namespace testing
+}  // namespace gvisor
diff --git a/test/util/BUILD b/test/util/BUILD
index a1b9ff526..c124cef34 100644
--- a/test/util/BUILD
+++ b/test/util/BUILD
@@ -184,6 +184,17 @@ cc_test(
 )
 
 cc_library(
+    name = "pty_util",
+    testonly = 1,
+    srcs = ["pty_util.cc"],
+    hdrs = ["pty_util.h"],
+    deps = [
+        ":file_descriptor",
+        ":posix_error",
+    ],
+)
+
+cc_library(
     name = "signal_util",
     testonly = 1,
     srcs = ["signal_util.cc"],
diff --git a/test/util/pty_util.cc b/test/util/pty_util.cc
new file mode 100644
index 000000000..c0fd9a095
--- /dev/null
+++ b/test/util/pty_util.cc
@@ -0,0 +1,45 @@
+// 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.
+
+#include "test/util/pty_util.h"
+
+#include <sys/ioctl.h>
+#include <termios.h>
+
+#include "test/util/file_descriptor.h"
+#include "test/util/posix_error.h"
+
+namespace gvisor {
+namespace testing {
+
+PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master) {
+  // Get pty index.
+  int n;
+  int ret = ioctl(master.get(), TIOCGPTN, &n);
+  if (ret < 0) {
+    return PosixError(errno, "ioctl(TIOCGPTN) failed");
+  }
+
+  // Unlock pts.
+  int unlock = 0;
+  ret = ioctl(master.get(), TIOCSPTLCK, &unlock);
+  if (ret < 0) {
+    return PosixError(errno, "ioctl(TIOSPTLCK) failed");
+  }
+
+  return Open(absl::StrCat("/dev/pts/", n), O_RDWR | O_NONBLOCK);
+}
+
+}  // namespace testing
+}  // namespace gvisor
diff --git a/test/util/pty_util.h b/test/util/pty_util.h
new file mode 100644
index 000000000..367b14f15
--- /dev/null
+++ b/test/util/pty_util.h
@@ -0,0 +1,30 @@
+// 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.
+
+#ifndef GVISOR_TEST_UTIL_PTY_UTIL_H_
+#define GVISOR_TEST_UTIL_PTY_UTIL_H_
+
+#include "test/util/file_descriptor.h"
+#include "test/util/posix_error.h"
+
+namespace gvisor {
+namespace testing {
+
+// Opens the slave end of the passed master as R/W and nonblocking.
+PosixErrorOr<FileDescriptor> OpenSlave(const FileDescriptor& master);
+
+}  // namespace testing
+}  // namespace gvisor
+
+#endif  // GVISOR_TEST_UTIL_PTY_UTIL_H_