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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 8A464C2D0BE for ; Sun, 8 Dec 2019 13:57:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B1B8206F4 for ; Sun, 8 Dec 2019 13:57:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726987AbfLHN5Y (ORCPT ); Sun, 8 Dec 2019 08:57:24 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60170 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726728AbfLHNym (ORCPT ); Sun, 8 Dec 2019 08:54:42 -0500 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1idx1C-0007dm-3l; Sun, 08 Dec 2019 13:54:38 +0000 Received: from ben by deadeye with local (Exim 4.93-RC1) (envelope-from ) id 1idx1B-0002MA-4R; Sun, 08 Dec 2019 13:54:37 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "syzbot" , "Tetsuo Handa" , "Greg Kroah-Hartman" Date: Sun, 08 Dec 2019 13:53:06 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 22/72] /dev/mem: Bail out upon SIGKILL. In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 3.16.79-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa commit 8619e5bdeee8b2c685d686281f2d2a6017c4bc15 upstream. syzbot found that a thread can stall for minutes inside read_mem() or write_mem() after that thread was killed by SIGKILL [1]. Reading from iomem areas of /dev/mem can be slow, depending on the hardware. While reading 2GB at one read() is legal, delaying termination of killed thread for minutes is bad. Thus, allow reading/writing /dev/mem and /dev/kmem to be preemptible and killable. [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632 [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536 [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440 [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344 [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248 Theoretically, reading/writing /dev/mem and /dev/kmem can become "interruptible". But this patch chose "killable". Future patch will make them "interruptible" so that we can revert to "killable" if some program regressed. [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e Signed-off-by: Tetsuo Handa Reported-by: syzbot Link: https://lore.kernel.org/r/1566825205-10703-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/char/mem.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -96,6 +96,13 @@ void __weak unxlate_dev_mem_ptr(unsigned { } +static inline bool should_stop_iteration(void) +{ + if (need_resched()) + cond_resched(); + return fatal_signal_pending(current); +} + /* * This funcion reads the *physical* memory. The f_pos points directly to the * memory location. @@ -162,6 +169,8 @@ static ssize_t read_mem(struct file *fil p += sz; count -= sz; read += sz; + if (should_stop_iteration()) + break; } *ppos += read; @@ -233,6 +242,8 @@ static ssize_t write_mem(struct file *fi p += sz; count -= sz; written += sz; + if (should_stop_iteration()) + break; } *ppos += written; @@ -436,6 +447,10 @@ static ssize_t read_kmem(struct file *fi read += sz; low_count -= sz; count -= sz; + if (should_stop_iteration()) { + count = 0; + break; + } } } @@ -460,6 +475,8 @@ static ssize_t read_kmem(struct file *fi buf += sz; read += sz; p += sz; + if (should_stop_iteration()) + break; } free_page((unsigned long)kbuf); } @@ -510,6 +527,8 @@ static ssize_t do_write_kmem(unsigned lo p += sz; count -= sz; written += sz; + if (should_stop_iteration()) + break; } *ppos += written; @@ -561,6 +580,8 @@ static ssize_t write_kmem(struct file *f buf += sz; virtr += sz; p += sz; + if (should_stop_iteration()) + break; } free_page((unsigned long)kbuf); }