netdev - Re: Suspicious RCU usage in bridge with Linux v4.0-9362-g1fc149933fd4

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:	Mon, 04 May 2015 22:32:04 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>,
	Cong Wang <cwang@...pensource.com>
CC:	Dominick Grift <dac.override@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Suspicious RCU usage in bridge with Linux v4.0-9362-g1fc149933fd4

On 05/04/2015 04:27 PM, Stephen Hemminger wrote:
> On Mon, 4 May 2015 11:45:41 -0700
> Cong Wang <cwang@...pensource.com> wrote:
> 
>> On Mon, May 4, 2015 at 6:39 AM, Dominick Grift <dac.override@...il.com> wrote:
>>> On Thu, Apr 23, 2015 at 01:07:45PM -0400, Josh Boyer wrote:
>>>> Hi All,
>>>>
>>>> We've had a user report the following backtrace from the bridge module
>>>> with a recent Linus' tree.  Has anything like this been reported yet?
>>>> If you have any questions on setup, the user is CC'd.
>>>>
>>>> josh
>>>>
>>>> [   29.382235] br0: port 1(tap0) entered forwarding state
>>>>
>>>> [   29.382286] ===============================
>>>> [   29.382315] [ INFO: suspicious RCU usage. ]
>>>> [   29.382344] 4.1.0-0.rc0.git11.1.fc23.x86_64 #1 Not tainted
>>>> [   29.382380] -------------------------------
>>>> [   29.382409] net/bridge/br_private.h:626 suspicious
>>>> rcu_dereference_check() usage!
>>>
>>> <snip>
>>>
>>> With 4.1.0-0.rc1.git1.1.fc23.x86_64 the situation seems to have slightly changed:
>>>
>>
>> Should be the same issue. Please give the attached patch a try,
>> it is compile-tested only.
>>
>> Thanks!
> 
> Good analysis in identifying the issue. But the proposed patch
> doesn't seem right.
> 
> The br->lock protects against changes to the bridge port state.
> vlan_info should be treated as part of the bridge state.
> 
> The correct fix is to get vlan_info out of depending on RTNL
> and use br->lock to control modifications.
> 

Changing the write side protection to be dependent on br->lock would
then require rcu or lock to be held in br_getlink().  It all
boils down to the same thing.  br_fill_info() needs to be either
in rcu or locked context.  It's already in rtnl context, so Eric's
proposal is the simplest one.

-vlad

> --
> 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
> 

--
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