[PATCH] pid-sandbox: Forward SIGTSTP and SIGCONT (bug 704498)

For correct operation of Ctrl+Z, forward SIGTSTP and SIGCONT
to all sandboxed pids.

Fixes: 37e4dc5ae842 ("pid-sandbox: pid-ns-init setsid support (bug 675870)")
Bug: https://bugs.gentoo.org/704498
Signed-off-by: Zac Medico <[email protected]>
---
 bin/pid-ns-init | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/bin/pid-ns-init b/bin/pid-ns-init
index 3a218a5df..e410dd028 100644
--- a/bin/pid-ns-init
+++ b/bin/pid-ns-init
@@ -1,5 +1,5 @@
 #!/usr/bin/env python
-# Copyright 2018-2019 Gentoo Authors
+# Copyright 2018-2020 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 import errno
@@ -19,6 +19,11 @@ KILL_SIGNALS = (
 	signal.SIGHUP,
 )
 
+SIGTSTP_SIGCONT = (
+	signal.SIGTSTP,
+	signal.SIGCONT,
+)
+
 
 def forward_kill_signal(pid, signum, frame):
 	if pid == 0:
@@ -28,6 +33,18 @@ def forward_kill_signal(pid, signum, frame):
 	os.kill(pid, signum)
 
 
+def forward_sigtstp_sigcont(pid, signum, frame):
+	handler = None
+	if pid == 0:
+		# Temporarily disable the handler in order to prevent it from
+		# being called recursively, since the signal will also be sent
+		# to the current process.
+		handler = signal.signal(signum, signal.SIG_DFL)
+	os.kill(pid, signum)
+	if handler is not None:
+		signal.signal(signum, handler)
+
+
 def preexec_fn(uid, gid, groups, umask):
 	if gid is not None:
 		os.setgid(gid)
@@ -97,6 +114,11 @@ def main(argv):
 	for signum in KILL_SIGNALS:
 		signal.signal(signum, sig_handler)
 
+	# For correct operation of Ctrl+Z, forward SIGTSTP and SIGCONT.
+	sigtstp_sigcont_handler = functools.partial(forward_sigtstp_sigcont, 0 if setsid else main_child_pid)
+	for signum in SIGTSTP_SIGCONT:
+		signal.signal(signum, sigtstp_sigcont_handler)
+
 	# wait for child processes
 	while True:
 		try:
-- 
2.26.2