Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161143AbWJKQyx (ORCPT ); Wed, 11 Oct 2006 12:54:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161144AbWJKQyx (ORCPT ); Wed, 11 Oct 2006 12:54:53 -0400 Received: from hu-out-0506.google.com ([72.14.214.239]:4392 "EHLO hu-out-0506.google.com") by vger.kernel.org with ESMTP id S1161143AbWJKQyx (ORCPT ); Wed, 11 Oct 2006 12:54:53 -0400 Message-ID: <474c7c2f0610110954y46b68a14q17b88a5e28ffe8d9@mail.gmail.com> Date: Wed, 11 Oct 2006 12:54:51 -0400 From: "=?UTF-8?Q?G=C3=BCnther_Starnberger?=" To: linux-kernel@vger.kernel.org Subject: Userspace process may be able to DoS kernel MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2788 Lines: 60 [I'm not subscribed on this list - please CC answers to me.] Hello, It seems that the latest version of Skype may exhibit a problem in the kernel where a non-root userspace process is able to block the whole system for durations of up to several minutes. If someone is able to reproduce the steps which cause the problem he may be able to DoS a system by consecutively causing soft lockups. There were some reports of this problem on other lists before, but mostly on tainted systems. I was able to reproduce this problem on a non-tainted mostly vanilla 2.6.17.6 kernel (it includes the suspend2 patches). As most users who reported this problem are using Ubuntu, the problem may be related to one of the settings in Ubuntu's kernel config. The configuration of my kernel is also based on the Ubuntu kernel config. As I am not using the patched kernel by Ubuntu I hope that the LKML is the right place to report this issue. The lockup usually occurs when Skype 1.3.x for Linux (I'm using 1.3.0.53) sits around idle for some time and then (presumably) uses the sound device (i.e. for me it happens when I call a contact - others reported this problem occurs for incoming messages [there may be an audio notification of the messages enabled]). The lockup can take from several seconds (where it is not detected by the kernel) up to some minutes. The whole system seems to be blocked - i.e. there is not even disk IO. dmesg reports the following: BUG: soft lockup detected on CPU#0! softlockup_tick+0xad/0xf0 update_process_times+0x39/0x90 smp_apic_timer_interrupt+0x5b/0x70 get_offset_pmtmr+0x97/0x1060 apic_timer_interrupt+0x1c/0x24 hrtimer_get_res+0x0/0x60 get_offset_pmtmr+0x97/0x1060 do_gettimeofday+0x1f/0xd0 getnstimeofday+0x14/0x40 sys_clock_gettime+0x31/0xb0 sysenter_past_esp+0x54/0x75 A copy of my kernel config is available at: http://virtual.sysfrog.org/~gst/config.txt The hardware where this problem occurs here is a X41 Thinkpad (Pentium M Dothan). There are also reports on other non-Intel CPUs e.g. AMD Turion 64. Please see the more extensive documentation of this problem on https://launchpad.net/distros/ubuntu/+source/linux-source-2.6.15/+bug/53216 (although some of the people there use tainted kernels). I will upgrade my 2.6.17.6 kernel to 2.6.18 and try to reproduce the problem there in the following days (but I fear that I won't have much time before the weekend). bye, /gst - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/