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:	Fri, 01 Jul 2011 14:20:44 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, rjw@...k.pl
Subject: Re: Linux 3.0 oopses when pulling a USB CDROM

On Fri, 2011-07-01 at 10:05 -0700, Andi Kleen wrote:
> Hi,
> 
> I found I can reliably crash a 3.0 system by pulling the
> USB cable of a mounted USB cdrom (or rather a USB device which
> has a builtin fake CD-ROM) 
> 
> I suspect it's a regression too.
> 
> It ends with a NULL pointer reference on a NULL sdev in 
> scsi_prep_state_check. 
> 
> Here's a somewhat incomplete backtrace (written down by hand)
> 
> scsi_prep_state_check
> scsi_setup_blk_pc_cmnd
> blk_peek_request
> ...
> scsi_request_fn
> ...
> ioctl_internal_command
> ...
> scsi_set_medium_removal
> sr_lock_door
> cdrom_release
> ...
> umount
> 
> I tried adding a 
> 
> 	if (!sdev) 
> 		return BLKPREP_KILL;
> 
> to scsi_prep_state_check, but that caused a RCU CPU stall 
> and a generally unhappy system instead.

Right, that wouldn't work.  The sdev in question comes from
request_queue->queuedata.  That only goes to null when the last
reference to the sdev has been released.  So the root cause is something
in sd holding a reference to sdev without actually getting an additional
refcount.

> The sdev must be still there in scsi_set_medium_removal because it's 
> referenced, so it must get lost somewhere in SCSI or in the block layer.
> 
> Any ideas how to fix this?

I'll see if I can find the refcounting problem.

Likely it's a longstanding bug which we didn't actually notice until
now.

James


--
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/