Merge pull request #6438 from gystemd:tcsetpgrp_SIGTTOU

PiperOrigin-RevId: 392774712

2 files changed, 88 insertions, 5 deletions

diff --git a/pkg/sentry/kernel/thread_group.go b/pkg/sentry/kernel/thread_group.go
index 2eda15303..5814a4eca 100644
--- a/pkg/sentry/kernel/thread_group.go
+++ b/pkg/sentry/kernel/thread_group.go
@@ -489,11 +489,6 @@ func (tg *ThreadGroup) SetForegroundProcessGroup(tty *TTY, pgid ProcessGroupID)
 	tg.signalHandlers.mu.Lock()
 	defer tg.signalHandlers.mu.Unlock()
 
-	// TODO(gvisor.dev/issue/6148): "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, linuxerr.ENOTTY
@@ -516,6 +511,16 @@ func (tg *ThreadGroup) SetForegroundProcessGroup(tty *TTY, pgid ProcessGroupID)
 		return -1, linuxerr.EPERM
 	}
 
+	signalAction := tg.signalHandlers.actions[linux.SIGTTOU]
+	// If the calling process is a member of a background group, a SIGTTOU
+	// signal is sent to all members of this background process group.
+	// We need also need to check whether it is ignoring or blocking SIGTTOU.
+	ignored := signalAction.Handler == linux.SIG_IGN
+	blocked := tg.leader.signalMask == linux.SignalSetOf(linux.SIGTTOU)
+	if tg.processGroup.id != tg.processGroup.session.foreground.id && !ignored && !blocked {
+		tg.leader.sendSignalLocked(SignalInfoPriv(linux.SIGTTOU), true)
+	}
+
 	tg.processGroup.session.foreground.id = pgid
 	return 0, nil
 }
diff --git a/test/syscalls/linux/pty.cc b/test/syscalls/linux/pty.cc
index 5ff1f12a0..c008c89e7 100644
--- a/test/syscalls/linux/pty.cc
+++ b/test/syscalls/linux/pty.cc
@@ -1640,6 +1640,84 @@ TEST_F(JobControlTest, DISABLED_SetForegroundProcessGroup) {
   ASSERT_NO_ERRNO(res);
 }
 
+// This test verifies if a SIGTTOU signal is sent to the calling process's group
+// when tcsetpgrp is called by a background process
+TEST_F(JobControlTest, SetForegroundProcessGroupSIGTTOUBackground) {
+  auto res = RunInChild([=]() {
+    TEST_PCHECK(setsid() >= 0);
+    TEST_PCHECK(!ioctl(replica_.get(), TIOCSCTTY, 0));
+    pid_t grandchild = fork();
+    if (!grandchild) {
+      // Assign a different pgid to the child so it will result as
+      // a background process.
+      TEST_PCHECK(!setpgid(grandchild, getpid()));
+      TEST_PCHECK(!tcsetpgrp(replica_.get(), getpgid(0)));
+      // We should never reach this.
+      _exit(1);
+    }
+    int wstatus;
+    TEST_PCHECK(waitpid(grandchild, &wstatus, WSTOPPED) == grandchild);
+    TEST_PCHECK(WSTOPSIG(wstatus) == SIGTTOU);
+  });
+  ASSERT_NO_ERRNO(res);
+}
+
+// This test verifies that a SIGTTOU signal is not delivered to
+// a background process which calls tcsetpgrp and is ignoring SIGTTOU
+TEST_F(JobControlTest, SetForegroundProcessGroupSIGTTOUIgnored) {
+  auto res = RunInChild([=]() {
+    TEST_PCHECK(setsid() >= 0);
+    TEST_PCHECK(!ioctl(replica_.get(), TIOCSCTTY, 0));
+    pid_t grandchild = fork();
+    if (!grandchild) {
+      // Ignore SIGTTOU so the child in background won't
+      // be stopped when it will call tcsetpgrp
+      struct sigaction sa = {};
+      sa.sa_handler = SIG_IGN;
+      sa.sa_flags = 0;
+      sigemptyset(&sa.sa_mask);
+      sigaction(SIGTTOU, &sa, NULL);
+      // Assign a different pgid to the child so it will result as
+      // a background process.
+      TEST_PCHECK(!setpgid(grandchild, getpid()));
+      TEST_PCHECK(!tcsetpgrp(replica_.get(), getpgid(0)));
+      _exit(0);
+    }
+    int wstatus;
+    TEST_PCHECK(waitpid(grandchild, &wstatus, WSTOPPED) == grandchild);
+    TEST_PCHECK(WSTOPSIG(wstatus) != SIGTTOU);
+    TEST_PCHECK(WIFEXITED(wstatus));
+  });
+  ASSERT_NO_ERRNO(res);
+}
+
+// This test verifies that a SIGTTOU signal is not delivered to
+// a background process which calls tcsetpgrp and is blocking SIGTTOU
+TEST_F(JobControlTest, SetForegroundProcessGroupSIGTTOUBlocked) {
+  auto res = RunInChild([=]() {
+    TEST_PCHECK(setsid() >= 0);
+    TEST_PCHECK(!ioctl(replica_.get(), TIOCSCTTY, 0));
+    pid_t grandchild = fork();
+    if (!grandchild) {
+      // Block SIGTTOU so the child in background won't
+      // be stopped when it will call tcsetpgrp
+      sigset_t signal_set;
+      sigemptyset(&signal_set);
+      sigaddset(&signal_set, SIGTTOU);
+      sigprocmask(SIG_BLOCK, &signal_set, NULL);
+      // Assign a different pgid to the child so it will result as
+      // a background process.
+      TEST_PCHECK(!setpgid(grandchild, getpid()));
+      TEST_PCHECK(!tcsetpgrp(replica_.get(), getpgid(0)));
+      _exit(0);
+    }
+    int wstatus;
+    TEST_PCHECK(waitpid(grandchild, &wstatus, WSTOPPED) == grandchild);
+    TEST_PCHECK(WSTOPSIG(wstatus) != SIGTTOU);
+  });
+  ASSERT_NO_ERRNO(res);
+}
+
 TEST_F(JobControlTest, SetForegroundProcessGroupWrongTTY) {
   pid_t pid = getpid();
   ASSERT_THAT(ioctl(replica_.get(), TIOCSPGRP, &pid),