Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933004AbeAHNBt (ORCPT + 1 other); Mon, 8 Jan 2018 08:01:49 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:44074 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932900AbeAHNBp (ORCPT ); Mon, 8 Jan 2018 08:01:45 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Oleg Nesterov , Dmitry Vyukov , Kyle Huey , Kees Cook , Andrew Morton , Linus Torvalds Subject: [PATCH 4.9 11/21] kernel/signal.c: remove the no longer needed SIGNAL_UNKILLABLE check in complete_signal() Date: Mon, 8 Jan 2018 13:59:31 +0100 Message-Id: <20180108125920.714493257@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180108125920.106264989@linuxfoundation.org> References: <20180108125920.106264989@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 426915796ccaf9c2bd9bb06dc5702225957bc2e5 upstream. complete_signal() checks SIGNAL_UNKILLABLE before it starts to destroy the thread group, today this is wrong in many ways. If nothing else, fatal_signal_pending() should always imply that the whole thread group (except ->group_exit_task if it is not NULL) is killed, this check breaks the rule. After the previous changes we can rely on sig_task_ignored(); sig_fatal(sig) && SIGNAL_UNKILLABLE can only be true if we actually want to kill this task and sig == SIGKILL OR it is traced and debugger can intercept the signal. This should hopefully fix the problem reported by Dmitry. This test-case static int init(void *arg) { for (;;) pause(); } int main(void) { char stack[16 * 1024]; for (;;) { int pid = clone(init, stack + sizeof(stack)/2, CLONE_NEWPID | SIGCHLD, NULL); assert(pid > 0); assert(ptrace(PTRACE_ATTACH, pid, 0, 0) == 0); assert(waitpid(-1, NULL, WSTOPPED) == pid); assert(ptrace(PTRACE_DETACH, pid, 0, SIGSTOP) == 0); assert(syscall(__NR_tkill, pid, SIGKILL) == 0); assert(pid == wait(NULL)); } } triggers the WARN_ON_ONCE(!(task->jobctl & JOBCTL_STOP_PENDING)) in task_participate_group_stop(). do_signal_stop()->signal_group_exit() checks SIGNAL_GROUP_EXIT and return false, but task_set_jobctl_pending() checks fatal_signal_pending() and does not set JOBCTL_STOP_PENDING. And his should fix the minor security problem reported by Kyle, SECCOMP_RET_TRACE can miss fatal_signal_pending() the same way if the task is the root of a pid namespace. Link: http://lkml.kernel.org/r/20171103184246.GD21036@redhat.com Signed-off-by: Oleg Nesterov Reported-by: Dmitry Vyukov Reported-by: Kyle Huey Reviewed-by: Kees Cook Tested-by: Kyle Huey Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/signal.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/kernel/signal.c +++ b/kernel/signal.c @@ -919,9 +919,9 @@ static void complete_signal(int sig, str * then start taking the whole group down immediately. */ if (sig_fatal(p, sig) && - !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) && + !(signal->flags & SIGNAL_GROUP_EXIT) && !sigismember(&t->real_blocked, sig) && - (sig == SIGKILL || !t->ptrace)) { + (sig == SIGKILL || !p->ptrace)) { /* * This signal will be fatal to the whole group. */