netdev - Re: [PATCH 04/10] AOE: use rcu to find network device

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]

Message-ID: <20091110150617.0e6920f0@nehalam>
Date:	Tue, 10 Nov 2009 15:06:17 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Ed Cashin <ecashin@...aid.com>
Cc:	davem@...emloft.net, ecashin@...aid.com, harvey.harrison@...il.com,
	bzolnier@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 04/10] AOE: use rcu to find network device

On Tue, 10 Nov 2009 15:01:49 -0500
Ed Cashin <ecashin@...aid.com> wrote:

> On Tue Nov 10 13:07:37 EST 2009, shemminger@...tta.com wrote:
> > This gets rid of another use of read_lock(&dev_base_lock) by using
> > RCU. Also, it only increments the reference count of the device actually
> > used rather than holding and releasing every device
> > 
> > Compile tested only.
> 
> This function runs once a minute when the aoe driver is loaded,
> if you'd like to test it a bit more.
> 
> It looks like there's no dev_put corresponding to the dev_hold
> after the changes.
> 

Hmm, looks like AOE actually is not ref counting the network device.
So my patch is incorrect. 

As it stands (before my patch), it is UNSAFE. It can decide to queue
packets to a device that is removed out from underneath it causing
reference to freed memory.

Moving the rcu_read_lock up to aoecmd_cfg() would solve that but the
whole driver appears to be unsafe about device refcounting and handling
device removal properly.  

It needs to:

1. Get a device ref count when it remembers a device: (ie addif)
2. Install a notifier that looks for device removal events
3. In notifier, remove interface, including flushing all pending
   skb's for that device.

This obviously is beyond the scope of the RCU stuff.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html