netdev - RE: [PATCH net v2] ravb: Fix races between ravb_tx_timeout

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Date: Thu, 16 Nov 2023 02:15:57 +0000
From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To: Sergey Shtylyov <s.shtylyov@....ru>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH net v2] ravb: Fix races between ravb_tx_timeout_work() and
 net related ops

Hello,

> From: Sergey Shtylyov, Sent: Thursday, November 16, 2023 3:31 AM
> 
> On 11/15/23 5:09 AM, Yoshihiro Shimoda wrote:
> [...]
> 
> >>> Fix races between ravb_tx_timeout_work() and functions of net_device_ops
> >>> and ethtool_ops by using rtnl_trylock() and rtnl_unlock(). Note that
> >>> since ravb_close() is under the rtnl lock and calls cancel_work_sync(),
> >>> ravb_tx_timeout_work() should calls rtnl_trylock(). Otherwise, a deadlock
> >>> may happen in ravb_tx_timeout_work() like below:
> >>>
> >>> CPU0			CPU1
> >>> 			ravb_tx_timeout()
> >>> 			schedule_work()
> >>> ...
> >>> __dev_close_many()
> >>> // Under rtnl lock
> >>> ravb_close()
> >>> cancel_work_sync()
> >>> // Waiting
> >>> 			ravb_tx_timeout_work()
> >>> 			rtnl_lock()
> >>> 			// This is possible to cause a deadlock
> >>>
> >>> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> >>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> >>
> >> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
> 
> [...]
> 
> >>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> >>> index 0ef0b88b7145..300c1885e1e1 100644
> >>> --- a/drivers/net/ethernet/renesas/ravb_main.c
> >>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> >>> @@ -1874,6 +1874,9 @@ static void ravb_tx_timeout_work(struct work_struct *work)
> >>>  	struct net_device *ndev = priv->ndev;
> >>>  	int error;
> >>>
> >>> +	if (!rtnl_trylock())
> >>> +		return;
> >>
> >>    I wonder if we should reschedule the work here...
> >
> > I think so. But, it should reschedule the work if the netif is still running because
> > Use-after-free issue happens again when cancel_work_sync() is calling. Also, I also think
> > we should use schedule_delayed_work() instead. So, I'll submit such a patch as v3.
> 
>    I'm not really sure about that one. Note that cancel_work_sync() should
> work with the works requeueing themselves, the comments say...

I'm sorry, I completely mistook to explain this... I should have said:
It should not reschedule the work if the netif is not running because
          ~~~                                     ~~~
use-after-free issue happens again when cancel_work_sync() is called from ravb_remove().
                                                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Also, I completely misunderstood the behavior of cancel_{schedule_}work_sync().
In the function(s), since WORK_STRUCT_PENDING_BIT is set, schedule_{delayed_}work()
will not schedule the work anymore. So, I'll drop a condition netif_running()
from the ravb_tx_timeout_work().

Best regards,
Yoshihiro Shimoda


> > Best regards,
> > Yoshihiro Shimoda
> 
> [...]
> 
> MBR, Sergey