Re: [PATCH net-next v3] net: phy: Fix suspicious rcu_dereference usage

Hi, Kory,

On 21.01.2025 18:11, Kory Maincent wrote:

On Tue, 21 Jan 2025 15:44:34 +0000
Paul Barker [off-list ref] wrote:

quoted

On 21/01/2025 13:01, Kory Maincent wrote:

quoted

On Tue, 21 Jan 2025 11:34:48 +0000
Paul Barker [off-list ref] wrote:
  

quoted

On 21/01/2025 09:38, Kory Maincent wrote:  

 [...]  
 [...]  

quoted

quoted

 [...]    

 [...]  
 [...]  

quoted

quoted

(Cc'ing Niklas and Sergey as this relates to the ravb driver)  

Yes, thanks.
  

quoted

Why do we need to hold the rtnl mutex across the calls to
netif_device_detach() and ravb_wol_setup()?

My reading of Documentation/networking/netdevices.rst is that the rtnl
mutex is held when the net subsystem calls the driver's ndo_stop method,
which in our case is ravb_close(). So, we should take the rtnl mutex
when we call ravb_close() directly, in both ravb_suspend() and
ravb_wol_restore(). That would ensure that we do not call
phy_disconnect() without holding the rtnl mutex and should fix this
issue.  

Not sure about it. For example ravb_ptp_stop() called in ravb_wol_setup()
won't be protected by the rtnl lock.  

ravb_ptp_stop() modifies a couple of device registers and calls
ptp_clock_unregister(). I don't see anything to suggest that this
requires the rtnl lock to be held, unless I am missing something.

What happens if two ptp_clock_unregister() with the same ptp_clock pointer are 
called simultaneously? From ravb_suspend and ravb_set_ringparam for example. It
may cause some errors.

Can this happen? I see ethtool_ops::set_ringparam() references only in
ethtool or ioctl files:

net/ethtool/ioctl.c:2066
net/ethtool/ioctl.c:2081
net/ethtool/rings.c:212
net/ethtool/rings.c:304

At the time the suspend/resume APIs are called the user space threads are
frozen.

Thank you,
Claudiu

For example the ptp->kworker pointer could be used after a kfree.
https://elixir.bootlin.com/linux/v6.12.6/source/drivers/ptp/ptp_clock.c#L416

Regards,