From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:54722 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726343AbeHUJlY (ORCPT ); Tue, 21 Aug 2018 05:41:24 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+619d9f40141d826b097e@syzkaller.appspotmail.com, Takashi Iwai Subject: [PATCH 4.18 08/35] ALSA: virmidi: Fix too long output trigger loop Date: Tue, 21 Aug 2018 08:20:34 +0200 Message-Id: <20180821055020.350192028@linuxfoundation.org> In-Reply-To: <20180821055019.954904905@linuxfoundation.org> References: <20180821055019.954904905@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit 50e9ffb1996a5d11ff5040a266585bad4ceeca0a upstream. The virmidi output trigger tries to parse the all available bytes and process sequencer events as much as possible. In a normal situation, this is supposed to be relatively short, but a program may give a huge buffer and it'll take a long time in a single spin lock, which may eventually lead to a soft lockup. This patch simply adds a workaround, a cond_resched() call in the loop if applicable. A better solution would be to move the event processor into a work, but let's put a duct-tape quickly at first. Reported-and-tested-by: Dae R. Jeong Reported-by: syzbot+619d9f40141d826b097e@syzkaller.appspotmail.com Cc: Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/seq/seq_virmidi.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -163,6 +163,7 @@ static void snd_virmidi_output_trigger(s int count, res; unsigned char buf[32], *pbuf; unsigned long flags; + bool check_resched = !in_atomic(); if (up) { vmidi->trigger = 1; @@ -200,6 +201,15 @@ static void snd_virmidi_output_trigger(s vmidi->event.type = SNDRV_SEQ_EVENT_NONE; } } + if (!check_resched) + continue; + /* do temporary unlock & cond_resched() for avoiding + * CPU soft lockup, which may happen via a write from + * a huge rawmidi buffer + */ + spin_unlock_irqrestore(&substream->runtime->lock, flags); + cond_resched(); + spin_lock_irqsave(&substream->runtime->lock, flags); } out: spin_unlock_irqrestore(&substream->runtime->lock, flags);