| 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
| ||
|
Message-ID: <4a65e53c-f13b-9cc3-bffa-f2f2aae423b9@gmail.com>
Date: Wed, 6 Sep 2017 15:51:36 -0700
From: David Daney <ddaney.cavm@...il.com>
To: David Daney <ddaney@...iumnetworks.com>,
Florian Fainelli <f.fainelli@...il.com>,
Mason <slash.tmp@...e.fr>
Cc: Marc Gonzalez <marc_gonzalez@...madesigns.com>,
netdev <netdev@...r.kernel.org>,
Geert Uytterhoeven <geert+renesas@...der.be>,
David Miller <davem@...emloft.net>,
Andrew Lunn <andrew@...n.ch>, Mans Rullgard <mans@...sr.com>
Subject: Re: [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in
phy_stop_machine()"
On 09/06/2017 01:49 PM, David Daney wrote:
> On 09/06/2017 11:59 AM, Florian Fainelli wrote:
>> On 09/06/2017 11:00 AM, David Daney wrote:
>>> On 08/31/2017 11:29 AM, Florian Fainelli wrote:
>>>> On 08/31/2017 11:12 AM, Mason wrote:
>>>>> On 31/08/2017 19:53, Florian Fainelli wrote:
>>>>>> On 08/31/2017 10:49 AM, Mason wrote:
>>>>>>> On 31/08/2017 18:57, Florian Fainelli wrote:
>>>>>>>> And the race is between phy_detach() setting phydev->attached_dev
>>>>>>>> = NULL
>>>>>>>> and phy_state_machine() running in PHY_HALTED state and calling
>>>>>>>> netif_carrier_off().
>>>>>>>
>>>>>>> I must be missing something.
>>>>>>> (Since a thread cannot race against itself.)
>>>>>>>
>>>>>>> phy_disconnect calls phy_stop_machine which
>>>>>>> 1) stops the work queue from running in a separate thread
>>>>>>> 2) calls phy_state_machine *synchronously*
>>>>>>> which runs the PHY_HALTED case with everything well-defined
>>>>>>> end of phy_stop_machine
>>>>>>>
>>>>>>> phy_disconnect only then calls phy_detach()
>>>>>>> which makes future calls of phy_state_machine perilous.
>>>>>>>
>>>>>>> This all happens in the same thread, so I'm not yet
>>>>>>> seeing where the race happens?
>>>>>>
>>>>>> The race is as described in David's earlier email, so let's recap:
>>>>>>
>>>>>> Thread 1 Thread 2
>>>>>> phy_disconnect()
>>>>>> phy_stop_interrupts()
>>>>>> phy_stop_machine()
>>>>>> phy_state_machine()
>>>>>> -> queue_delayed_work()
>>>>>> phy_detach()
>>>>>> phy_state_machine()
>>>>>> -> netif_carrier_off()
>>>>>>
>>>>>> If phy_detach() finishes earlier than the workqueue had a chance
>>>>>> to be
>>>>>> scheduled and process PHY_HALTED again, then we trigger the NULL
>>>>>> pointer
>>>>>> de-reference.
>>>>>>
>>>>>> workqueues are not tasklets, the CPU scheduling them gets no
>>>>>> guarantee
>>>>>> they will run on the same CPU.
>>>>>
>>>>> Something does not add up.
>>>>>
>>>>> The synchronous call to phy_state_machine() does:
>>>>>
>>>>> case PHY_HALTED:
>>>>> if (phydev->link) {
>>>>> phydev->link = 0;
>>>>> netif_carrier_off(phydev->attached_dev);
>>>>> phy_adjust_link(phydev);
>>>>> do_suspend = true;
>>>>> }
>>>>>
>>>>> then sets phydev->link = 0; therefore subsequent calls to
>>>>> phy_state_machin() will be no-op.
>>>>
>>>> Actually you are right, once phydev->link is set to 0 these would
>>>> become
>>>> no-ops. Still scratching my head as to what happens for David then...
>>>>
>>>>>
>>>>> Also, queue_delayed_work() is only called in polling mode.
>>>>> David stated that he's using interrupt mode.
>>>
>>> Did you see what I wrote?
>>
>> Still not following, see below.
>>
>>>
>>> phy_disconnect() calls phy_stop_interrupts() which puts it into polling
>>> mode. So the polling work gets queued unconditionally.
>>
>> What part of phy_stop_interrupts() is responsible for changing
>> phydev->irq to PHY_POLL? free_irq() cannot touch phydev->irq otherwise
>> subsequent request_irq() calls won't work anymore.
>> phy_disable_interrupts() only calls back into the PHY driver to
>> acknowledge and clear interrupts.
>>
>> If we were using a PHY with PHY_POLL, as Marc said, the first
>> synchronous call to phy_state_machine() would have acted on PHY_HALTED
>> and even if we incorrectly keep re-scheduling the state machine from
>> PHY_HALTED to PHY_HALTED the second time around nothing can happen.
>>
>> What are we missing here?
>>
>
> OK, I am now as confused as you guys are. I will go back and get an
> ftrace log out of the failure.
>
OK, let's forget about the PHY_HALTED discussion.
Consider instead the case of a Marvell phy with no interrupts connected
on a v4.9.43 kernel, single CPU:
0) | phy_disconnect() {
0) | phy_stop_machine() {
0) | cancel_delayed_work_sync() {
0) + 23.986 us | } /* cancel_delayed_work_sync */
0) | phy_state_machine() {
0) | phy_start_aneg_priv() {
0) | marvell_config_aneg() {
0) ! 240.538 us | } /* marvell_config_aneg */
0) ! 244.971 us | } /* phy_start_aneg_priv */
0) | queue_delayed_work_on() {
0) + 18.016 us | } /* queue_delayed_work_on */
0) ! 268.184 us | } /* phy_state_machine */
0) ! 297.394 us | } /* phy_stop_machine */
0) | phy_detach() {
0) | phy_suspend() {
0) | phy_ethtool_get_wol() {
0) 0.677 us | } /* phy_ethtool_get_wol */
0) | genphy_suspend() {
0) + 71.250 us | } /* genphy_suspend */
0) + 74.197 us | } /* phy_suspend */
0) + 80.302 us | } /* phy_detach */
0) ! 380.072 us | } /* phy_disconnect */
.
.
.
0) | process_one_work() {
0) | find_worker_executing_work() {
0) 0.688 us | } /* find_worker_executing_work */
0) | set_work_pool_and_clear_pending() {
0) 0.734 us | } /* set_work_pool_and_clear_pending */
0) | phy_state_machine() {
0) | genphy_read_status() {
0) ! 205.721 us | } /* genphy_read_status */
0) | netif_carrier_off() {
0) | do_page_fault() {
The do_page_fault() at the end indicates the NULL pointer dereference.
That added call to phy_state_machine() turns the polling back on
unconditionally for a phy that should be disconnected. How is that correct?
David.
Powered by blists - more mailing lists