From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D02AC3815B for ; Mon, 20 Apr 2020 17:08:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1999C206D9 for ; Mon, 20 Apr 2020 17:08:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726488AbgDTRIr (ORCPT ); Mon, 20 Apr 2020 13:08:47 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:55242 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725784AbgDTRIq (ORCPT ); Mon, 20 Apr 2020 13:08:46 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jQZuW-0000iW-C8; Mon, 20 Apr 2020 11:08:44 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jQZuV-0000LB-BN; Mon, 20 Apr 2020 11:08:44 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: linux-kernel@vger.kernel.org Cc: Christof Meerwald , Linux Containers , Oleg Nesterov References: <20200419201336.GI22017@edge.cmeerw.net> Date: Mon, 20 Apr 2020 12:05:38 -0500 In-Reply-To: <20200419201336.GI22017@edge.cmeerw.net> (Christof Meerwald's message of "Sun, 19 Apr 2020 22:13:36 +0200") Message-ID: <87sggyytnh.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jQZuV-0000LB-BN;;;mid=<87sggyytnh.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+ZpZqqqjLt+ygusWJr5B44stKiUvd5wvA= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify_parent X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christof Meerwald writes: > Hi, > > this is probably related to commit > 7a0cf094944e2540758b7f957eb6846d5126f535 (signal: Correct namespace > fixups of si_pid and si_uid). > > With a 5.6.5 kernel I am seeing SIGCHLD signals that don't include a > properly set si_pid field - this seems to happen for multi-threaded > child processes. > > A simple test program (based on the sample from the signalfd man page): > > #include > #include > #include > #include > #include > #include > > #define handle_error(msg) \ > do { perror(msg); exit(EXIT_FAILURE); } while (0) > > int main(int argc, char *argv[]) > { > sigset_t mask; > int sfd; > struct signalfd_siginfo fdsi; > ssize_t s; > > sigemptyset(&mask); > sigaddset(&mask, SIGCHLD); > > if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1) > handle_error("sigprocmask"); > > pid_t chldpid; > char *chldargv[] = { "./sfdclient", NULL }; > posix_spawn(&chldpid, "./sfdclient", NULL, NULL, chldargv, NULL); > > sfd = signalfd(-1, &mask, 0); > if (sfd == -1) > handle_error("signalfd"); > > for (;;) { > s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo)); > if (s != sizeof(struct signalfd_siginfo)) > handle_error("read"); > > if (fdsi.ssi_signo == SIGCHLD) { > printf("Got SIGCHLD %d %d %d %d\n", > fdsi.ssi_status, fdsi.ssi_code, > fdsi.ssi_uid, fdsi.ssi_pid); > return 0; > } else { > printf("Read unexpected signal\n"); > } > } > } > > > and a multi-threaded client to test with: > > #include > #include > > void *f(void *arg) > { > sleep(100); > } > > int main() > { > pthread_t t[8]; > > for (int i = 0; i != 8; ++i) > { > pthread_create(&t[i], NULL, f, NULL); > } > } > > I tried to do a bit of debugging and what seems to be happening is > that > > /* From an ancestor pid namespace? */ > if (!task_pid_nr_ns(current, task_active_pid_ns(t))) { > > fails inside task_pid_nr_ns because the check for "pid_alive" fails. > > This code seems to be called from do_notify_parent and there we > actually have "tsk != current" (I am assuming both are threads of the > current process?) I instrumented the code with a warning and received the following backtrace: > WARNING: CPU: 0 PID: 777 at kernel/pid.c:501 __task_pid_nr_ns.cold.6+0xc/0x15 > Modules linked in: > CPU: 0 PID: 777 Comm: sfdclient Not tainted 5.7.0-rc1userns+ #2924 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > RIP: 0010:__task_pid_nr_ns.cold.6+0xc/0x15 > Code: ff 66 90 48 83 ec 08 89 7c 24 04 48 8d 7e 08 48 8d 74 24 04 e8 9a b6 44 00 48 83 c4 08 c3 48 c7 c7 59 9f ac 82 e8 c2 c4 04 00 <0f> 0b e9 3fd > RSP: 0018:ffffc9000042fbf8 EFLAGS: 00010046 > RAX: 000000000000000c RBX: 0000000000000000 RCX: ffffc9000042faf4 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81193d29 > RBP: ffffc9000042fc18 R08: 0000000000000000 R09: 0000000000000001 > R10: 000000100f938416 R11: 0000000000000309 R12: ffff8880b941c140 > R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880b941c140 > FS: 0000000000000000(0000) GS:ffff8880bca00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f2e8c0a32e0 CR3: 0000000002e10000 CR4: 00000000000006f0 > Call Trace: > send_signal+0x1c8/0x310 > do_notify_parent+0x50f/0x550 > release_task.part.21+0x4fd/0x620 > do_exit+0x6f6/0xaf0 > do_group_exit+0x42/0xb0 > get_signal+0x13b/0xbb0 > do_signal+0x2b/0x670 > ? __audit_syscall_exit+0x24d/0x2b0 > ? rcu_read_lock_sched_held+0x4d/0x60 > ? kfree+0x24c/0x2b0 > do_syscall_64+0x176/0x640 > ? trace_hardirqs_off_thunk+0x1a/0x1c > entry_SYSCALL_64_after_hwframe+0x49/0xb3 The immediate problem is as Christof noticed that "pid_alive(current) == false". This happens because do_notify_parent is called from the last thread to exit in a process after that thread has been reaped. The bigger issue is that do_notify_parent can be called from any process that manages to wait on a thread of a multi-threaded process from wait_task_zombie. So any logic based upon current for do_notify_parent is just nonsense, as current can be pretty much anything. So change do_notify_parent to call __send_signal directly. Inspecting the code it appears this problem has existed since the pid namespace support started handling this case in 2.6.30. This fix only backports to 7a0cf094944e ("signal: Correct namespace fixups of si_pid and si_uid") where the problem logic was moved out of __send_signal and into send_signal. Cc: stable@vger.kernel.org Fixes: 6588c1e3ff01 ("signals: SI_USER: Masquerade si_pid when crossing pid ns boundary Ref: 921cf9f63089 ("signals: protect cinit from unblocked SIG_DFL signals") Link: https://lore.kernel.org/lkml/20200419201336.GI22017@edge.cmeerw.net/ Signed-off-by: "Eric W. Biederman" --- Unless someone has an objection I will apply this one and send it to Linus. kernel/signal.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/signal.c b/kernel/signal.c index 9899c5f91ee1..a88a89422227 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1993,8 +1993,12 @@ bool do_notify_parent(struct task_struct *tsk, int sig) if (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) sig = 0; } + /* + * Bypass send_signal as the si_pid and si_uid values have + * been generated in the parent's namespaces. + */ if (valid_signal(sig) && sig) - __group_send_sig_info(sig, &info, tsk->parent); + __send_signal(sig, &info, tsk->parent, PIDTYPE_TGID, false); __wake_up_parent(tsk, tsk->parent); spin_unlock_irqrestore(&psig->siglock, flags); -- 2.20.1