From patchwork Fri Jun 19 18:32:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 11614921 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BC4FE90 for ; Fri, 19 Jun 2020 18:37:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FB65217A0 for ; Fri, 19 Jun 2020 18:37:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388198AbgFSSg4 (ORCPT ); Fri, 19 Jun 2020 14:36:56 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:33192 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388040AbgFSSg4 (ORCPT ); Fri, 19 Jun 2020 14:36:56 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jmLsj-0003Gy-Jt; Fri, 19 Jun 2020 12:36:53 -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 1jmLsf-0005ZZ-7p; Fri, 19 Jun 2020 12:36:53 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Cc: , Linus Torvalds , Oleg Nesterov , Jann Horn , Kees Cook , Bernd Edlinger References: <87pn9u6h8c.fsf@x220.int.ebiederm.org> Date: Fri, 19 Jun 2020 13:32:30 -0500 In-Reply-To: <87pn9u6h8c.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Fri, 19 Jun 2020 13:30:27 -0500") Message-ID: <87k1026h4x.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1jmLsf-0005ZZ-7p;;;mid=<87k1026h4x.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX180/W4+QdDu1YmGu7uqp9HqSF67L0PvcJ4= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa01.xmission.com X-Spam-Level: ** X-Spam-Status: No, score=2.0 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,NO_DNS_FOR_FROM,T_TM2_M_HEADER_IN_MSG, T_TooManySym_01,T_TooManySym_02,XMNoVowels,XMSubLong autolearn=disabled version=3.4.2 X-Spam-Virus: No X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * 0.7 XMSubLong Long Subject * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 NO_DNS_FOR_FROM DNS: Envelope sender has no MX or A DNS records * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 0; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_02 5+ unique symbols in subject * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: ; sa01 0; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **; X-Spam-Relay-Country: X-Spam-Timing: total 4017 ms - load_scoreonly_sql: 0.03 (0.0%), signal_user_changed: 4.2 (0.1%), b_tie_ro: 2.9 (0.1%), parse: 1.09 (0.0%), extract_message_metadata: 12 (0.3%), get_uri_detail_list: 2.4 (0.1%), tests_pri_-1000: 2.6 (0.1%), tests_pri_-950: 1.07 (0.0%), tests_pri_-900: 0.89 (0.0%), tests_pri_-90: 53 (1.3%), check_bayes: 52 (1.3%), b_tokenize: 6 (0.1%), b_tok_get_all: 7 (0.2%), b_comp_prob: 1.81 (0.0%), b_tok_touch_all: 36 (0.9%), b_finish: 0.62 (0.0%), tests_pri_0: 3931 (97.9%), check_dkim_signature: 0.39 (0.0%), check_dkim_adsp: 3675 (91.5%), poll_dns_idle: 3671 (91.4%), tests_pri_10: 1.88 (0.0%), tests_pri_500: 6 (0.2%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH 1/2] exec: Don't set group_exit_task during a coredump X-Spam-Flag: No 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-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Instead test SIGNAL_GROUP_COREDUMP in signal_group_exit(). This results in clearer easier to understand logic. This makes the code easier to modify in the future as this leaves de_thread as the only user of group_exit_task. This is safe because there are only two places that set SIGNAL_GROUP_COREDUMP. In one place the code is setting SIGNAL_GROUP_EXIT and SIGNAL_GROUP_COREDUMP together with the result that signal_group_exit() will subsequently return true. In the other the location which is being changed SIGNAL_GROUP_COREDUMP is being set along with signal_group_exit, which also causes subsequent calls of signal_group_exit to return true. Thus testing SIGNAL_GROUP_COREDUMP in signal_group_exit() results in no change in behavior. Only signal_group_exit tests group_exit_task so leaving as NULL during a coredump and nothing uses the value of group_exit_task that the coredump sets. So not setting group_exit_task is safe during a coredump. I looked at the commit that introduced this behavior[1] and Oleg describes that he was setting group_exit_task simply to cause signal_group_exit to return true. So no surprises come from the history. Cc: Oleg Nesterov [1] 6cd8f0acae34 ("coredump: ensure that SIGKILL always kills the dumping thread") Signed-off-by: "Eric W. Biederman" --- fs/coredump.c | 2 -- include/linux/sched/signal.h | 2 +- 2 files changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/coredump.c b/fs/coredump.c index 7237f07ff6be..37b71c72ab3a 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -369,7 +369,6 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm, spin_lock_irq(&tsk->sighand->siglock); if (!signal_group_exit(tsk->signal)) { mm->core_state = core_state; - tsk->signal->group_exit_task = tsk; nr = zap_process(tsk, exit_code, 0); clear_tsk_thread_flag(tsk, TIF_SIGPENDING); } @@ -481,7 +480,6 @@ static void coredump_finish(struct mm_struct *mm, bool core_dumped) spin_lock_irq(¤t->sighand->siglock); if (core_dumped && !__fatal_signal_pending(current)) current->signal->group_exit_code |= 0x80; - current->signal->group_exit_task = NULL; current->signal->flags = SIGNAL_GROUP_EXIT; spin_unlock_irq(¤t->sighand->siglock); diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 0ee5e696c5d8..92c72f5db111 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -265,7 +265,7 @@ static inline void signal_set_stop_flags(struct signal_struct *sig, /* If true, all threads except ->group_exit_task have pending SIGKILL */ static inline int signal_group_exit(const struct signal_struct *sig) { - return (sig->flags & SIGNAL_GROUP_EXIT) || + return (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_GROUP_COREDUMP)) || (sig->group_exit_task != NULL); }