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=-11.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 692DAC282C2 for ; Wed, 13 Feb 2019 18:44:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FEDC222D2 for ; Wed, 13 Feb 2019 18:44:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550083498; bh=xVJBuDf6p754DYRJtacnpKR/3TIEEvUQtRdhtVGejdc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=zbBbSw9255WG0rFv2tv/OlbfsV/fIoTAefmahoSMuDVp2Yz16wbQ0la8H1Q4C/Hf1 FPdh100niikgVRtj1BPNhjBbh77X/ISeeWbi/OZq3ysWIgZX0440x8NNlobq4r6NA/ E0TexXy0avIVXR8gSSEdfJ1w17yG/PrrQaouPG98= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394026AbfBMSo5 (ORCPT ); Wed, 13 Feb 2019 13:44:57 -0500 Received: from mail.kernel.org ([198.145.29.99]:43564 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388313AbfBMSoy (ORCPT ); Wed, 13 Feb 2019 13:44:54 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 431A4222D3; Wed, 13 Feb 2019 18:44:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550083493; bh=xVJBuDf6p754DYRJtacnpKR/3TIEEvUQtRdhtVGejdc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IlLUpUFtI8iMYHF8/LhQnyTJHQHWPwpHTMGQNCk24SnDrwPwfP5DgceD8q622nPWU OKmW5qzWGwOWR5MHvudIP3l8Alb2FVMS2uMIVnvS200kQxEIo5DQ9OK7VWF/5tnypr nYJAkKamIejP3yS7Vr0cuXdKiVa8w4auhbRWk/VQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dmitry Vyukov , "Eric W. Biederman" Subject: [PATCH 4.20 11/50] signal: Always notice exiting tasks Date: Wed, 13 Feb 2019 19:38:16 +0100 Message-Id: <20190213183656.733725215@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190213183655.747168774@linuxfoundation.org> References: <20190213183655.747168774@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric W. Biederman commit 35634ffa1751b6efd8cf75010b509dcb0263e29b upstream. Recently syzkaller was able to create unkillablle processes by creating a timer that is delivered as a thread local signal on SIGHUP, and receiving SIGHUP SA_NODEFERER. Ultimately causing a loop failing to deliver SIGHUP but always trying. Upon examination it turns out part of the problem is actually most of the solution. Since 2.5 signal delivery has found all fatal signals, marked the signal group for death, and queued SIGKILL in every threads thread queue relying on signal->group_exit_code to preserve the information of which was the actual fatal signal. The conversion of all fatal signals to SIGKILL results in the synchronous signal heuristic in next_signal kicking in and preferring SIGHUP to SIGKILL. Which is especially problematic as all fatal signals have already been transformed into SIGKILL. Instead of dequeueing signals and depending upon SIGKILL to be the first signal dequeued, first test if the signal group has already been marked for death. This guarantees that nothing in the signal queue can prevent a process that needs to exit from exiting. Cc: stable@vger.kernel.org Tested-by: Dmitry Vyukov Reported-by: Dmitry Vyukov Ref: ebf5ebe31d2c ("[PATCH] signal-fixes-2.5.59-A4") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman --- kernel/signal.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2393,6 +2393,11 @@ relock: goto relock; } + /* Has this task already been marked for death? */ + ksig->info.si_signo = signr = SIGKILL; + if (signal_group_exit(signal)) + goto fatal; + for (;;) { struct k_sigaction *ka; @@ -2488,6 +2493,7 @@ relock: continue; } + fatal: spin_unlock_irq(&sighand->siglock); /*