Don't allow writing or reading to TTY unless process group is in foreground.

If a background process tries to read from a TTY, linux sends it a SIGTTIN
unless the signal is blocked or ignored, or the process group is an orphan, in
which case the syscall returns EIO.

See drivers/tty/n_tty.c:n_tty_read()=>job_control().

If a background process tries to write a TTY, set the termios, or set the
foreground process group, linux then sends a SIGTTOU. If the signal is ignored
or blocked, linux allows the write. If the process group is an orphan, the
syscall returns EIO.

See drivers/tty/tty_io.c:tty_check_change().

PiperOrigin-RevId: 234044367
Change-Id: I009461352ac4f3f11c5d42c43ac36bb0caa580f9

1 files changed, 11 insertions, 3 deletions

diff --git a/pkg/sentry/control/proc.go b/pkg/sentry/control/proc.go
index 923399fb2..e848def14 100644
--- a/pkg/sentry/control/proc.go
+++ b/pkg/sentry/control/proc.go
@@ -222,10 +222,18 @@ func (proc *Proc) execAsync(args *ExecArgs) (*kernel.ThreadGroup, kernel.ThreadI
 		return nil, 0, nil, err
 	}
 
-	if ttyFile == nil {
-		return tg, tid, nil, nil
+	var ttyFileOps *host.TTYFileOperations
+	if ttyFile != nil {
+		// Set the foreground process group on the TTY before starting
+		// the process.
+		ttyFileOps = ttyFile.FileOperations.(*host.TTYFileOperations)
+		ttyFileOps.InitForegroundProcessGroup(tg.ProcessGroup())
 	}
-	return tg, tid, ttyFile.FileOperations.(*host.TTYFileOperations), nil
+
+	// Start the newly created process.
+	proc.Kernel.StartProcess(tg)
+
+	return tg, tid, ttyFileOps, nil
 }
 
 // PsArgs is the set of arguments to ps.