From a8ebd17160ce364fac6647f223991a8f2f1924b9 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 20 Jul 2018 15:59:17 -0500 Subject: tty_io: Use group_send_sig_info in __do_SACK to note it is a session being killed Replace send_sig and force_sig in __do_SAK with group_send_sig_info the general helper for sending a signal to a process group. This is wordier but it allows specifying PIDTYPE_SID so that the signal code knows the signal went to a session. Both force_sig() and send_sig(..., 1) specify SEND_SIG_PRIV and the new call of group_send_sig_info does that explicitly. This is enough to ensure even a pid namespace init is killed. The global init remains unkillable. The guarantee that __do_SAK tries to provide is a clean path to login to a machine. As the global init is unkillable, if it chooses to hold open a tty it can violate this guarantee. A technique other than killing processes would be needed to provide this guarantee to userspace. The only difference between force_sig and send_sig when sending SIGKILL is that SIGNAL_UNKILLABLE is cleared. This has no affect on the processing of a signal sent with SEND_SIG_PRIV by any process, making it unnecessary, and not behavior that needs to be preserved. force_sig was used originally because it did not take as many locks as send_sig. Today send_sig, force_sig and group_send_sig_info take the same locks when delivering a signal. group_send_sig_info also contains a permission check that force_sig and send_sig do not. However the presence of SEND_SIG_PRIV makes the permission check a noop. So the permission check does not result in any behavioral differences. Signed-off-by: "Eric W. Biederman" --- drivers/tty/tty_io.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 32bc3e3fe4d3..6553247a761f 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2738,7 +2738,7 @@ void __do_SAK(struct tty_struct *tty) do_each_pid_task(session, PIDTYPE_SID, p) { tty_notice(tty, "SAK: killed process %d (%s): by session\n", task_pid_nr(p), p->comm); - send_sig(SIGKILL, p, 1); + group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_SID); } while_each_pid_task(session, PIDTYPE_SID, p); /* Now kill any processes that happen to have the tty open */ @@ -2746,7 +2746,7 @@ void __do_SAK(struct tty_struct *tty) if (p->signal->tty == tty) { tty_notice(tty, "SAK: killed process %d (%s): by controlling tty\n", task_pid_nr(p), p->comm); - send_sig(SIGKILL, p, 1); + group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_SID); continue; } task_lock(p); @@ -2754,7 +2754,7 @@ void __do_SAK(struct tty_struct *tty) if (i != 0) { tty_notice(tty, "SAK: killed process %d (%s): by fd#%d\n", task_pid_nr(p), p->comm, i - 1); - force_sig(SIGKILL, p); + group_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_SID); } task_unlock(p); } while_each_thread(g, p); -- cgit v1.2.3