linux-kernel - Re: Userspace process may be able to DoS kernel

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Date:	Fri, 13 Oct 2006 15:24:31 +0200
From:	Joerg Platte <lists@...sa.net>
To:	"Günther Starnberger" <gst@...frog.org>
Cc:	"Pekka Enberg" <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: Userspace process may be able to DoS kernel

Am Donnerstag, 12. Oktober 2006 22:25 schrieb Günther Starnberger:
Hi,

> According to [1] there are several anti-debugging techniques used in
> Skype. I.e. if it notices some sort of debugger it will crash (on
> purpose).

I know. I just wanted to know if I'm able to catch a blocking system call...

> [1]
> www.blackhat.com/presentations/bh-europe-06/bh-eu-06-biondi/bh-eu-06-biondi
>-up.pdf -

Here is my output from a longer lockup today. I can confirm, that pings and 
system time are not affected by the lockup. I didn't try to log in via ssh 
but I think that will not work, too.

Oct 13 15:11:08 localhost kernel: BUG: soft lockup detected on CPU#0!
Oct 13 15:11:08 localhost kernel:  [<c012f9d5>] softlockup_tick+0x89/0xa4
Oct 13 15:11:08 localhost kernel:  [<c011b458>] update_process_times+0x35/0x57
Oct 13 15:11:08 localhost kernel:  [<c01052c9>] timer_interrupt+0x35/0x64
Oct 13 15:11:08 localhost kernel:  [<c012fc13>] handle_IRQ_event+0x23/0x49
Oct 13 15:11:08 localhost kernel:  [<c012fe45>] __do_IRQ+0x7b/0xde
Oct 13 15:11:08 localhost kernel:  [<c010438a>] do_IRQ+0x40/0x4d
Oct 13 15:11:08 localhost kernel:  [<c0102d82>] common_interrupt+0x1a/0x20
Oct 13 15:11:08 localhost kernel:  [<c01e3f0e>] acpi_pm_read+0x7/0xf
Oct 13 15:11:09 localhost kernel:  [<c011a53d>] getnstimeofday+0x2b/0xac
Oct 13 15:11:09 localhost kernel:  [<c01226f4>] sys_clock_gettime+0x42/0x7e
Oct 13 15:11:09 localhost kernel:  [<c0102bfb>] syscall_call+0x7/0xb
Oct 13 15:11:09 localhost kernel: BUG: soft lockup detected on CPU#0!
Oct 13 15:11:09 localhost kernel:  [<c012f9d5>] softlockup_tick+0x89/0xa4
Oct 13 15:11:09 localhost kernel:  [<c011b458>] update_process_times+0x35/0x57
Oct 13 15:11:09 localhost kernel:  [<c01052c9>] timer_interrupt+0x35/0x64
Oct 13 15:11:09 localhost kernel:  [<c012fc13>] handle_IRQ_event+0x23/0x49
Oct 13 15:11:09 localhost kernel:  [<c012fe45>] __do_IRQ+0x7b/0xde
Oct 13 15:11:09 localhost kernel:  [<c010438a>] do_IRQ+0x40/0x4d
Oct 13 15:11:09 localhost kernel:  [<c0102d82>] common_interrupt+0x1a/0x20
Oct 13 15:11:09 localhost kernel:  [<c01e3f0e>] acpi_pm_read+0x7/0xf
Oct 13 15:11:09 localhost kernel:  [<c011a53d>] getnstimeofday+0x2b/0xac
Oct 13 15:11:09 localhost kernel:  [<c01226f4>] sys_clock_gettime+0x42/0x7e
Oct 13 15:11:09 localhost kernel:  [<c0102bfb>] syscall_call+0x7/0xb

Typically I have two lockups, a first longer one and then a shorter one. Then 
everything runs without any problems. 

regards,
Jörg

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