linux-kernel - Re: Linux 3.0 oopses when pulling a USB CDROM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 2 Jul 2011 16:05:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andi Kleen <andi@...stfloor.org>
cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Dave Jones <davej@...hat.com>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <axboe@...nel.dk>, <rjw@...k.pl>,
	<linux-usb@...r.kernel.org>
Subject: Re: Linux 3.0 oopses when pulling a USB CDROM

On Sat, 2 Jul 2011, Andi Kleen wrote:

> > And the transition after unplug goes
> > 
> > 13->12->10->8->7->6->5->3
> > 
> > implying we're missing put events.
> 
> Don't know why. I used this check (with trace_scsi_dev containing the name)
> in put_device:
> 
> if (trace_scsi && dev->type == &scsi_dev_type &&
>      trace_scsi_dev[0] == 0 || !strcmp(dev_name(dev), trace_scsi_dev))) {
> 	dev_printk ...

These extra puts could be coming from deep inside the device-model
core, where they operate directly on the underlying kobject instead of
going through put_device().  For example, removal of sysfs symlinks
could have this effect.

> If you want instrumentation somewhere else please let me know.
> 
> Maybe there simply isn't a put_device to 0 and the NULL pointer happens
> for some other reason?

On my system, at least, the scsi_device's refcount dropped to 0 at the 
right time.  That wasn't the problem.  The NULL pointer occurs because 
the request_queue is used after the scsi_device has been removed from 
visibility; among other things, __scsi_remove_device() sets 
sdev->request_queue->queuedata to NULL.

As the comment says, this causes the request function to reject all I/O 
requests -- but not before trying to dereference the NULL pointer!

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/