linux-kernel - Re: [PATCH] net: usb: r8152: Check used MAC passthrough address

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Date:   Wed, 5 Jan 2022 08:55:25 +0100
From:   Henning Schild <henning.schild@...mens.com>
To:     Aaron Ma <aaron.ma@...onical.com>
CC:     <kuba@...nel.org>, <linux-usb@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <davem@...emloft.net>, <hayeswang@...ltek.com>, <tiwai@...e.de>
Subject: Re: [PATCH] net: usb: r8152: Check used MAC passthrough address

Am Wed, 5 Jan 2022 15:38:51 +0800
schrieb Aaron Ma <aaron.ma@...onical.com>:

> On 1/5/22 15:32, Henning Schild wrote:
> > Am Wed, 5 Jan 2022 08:23:55 +0100
> > schrieb Henning Schild <henning.schild@...mens.com>:
> >   
> >> Hi Aaron,
> >>
> >> if this or something similar goes in, please add another patch to
> >> remove the left-over defines.
> >>  
> 
> Sure, I will do it.
> 
> >> Am Wed,  5 Jan 2022 14:17:47 +0800
> >> schrieb Aaron Ma <aaron.ma@...onical.com>:
> >>  
> >>> When plugin multiple r8152 ethernet dongles to Lenovo Docks
> >>> or USB hub, MAC passthrough address from BIOS should be
> >>> checked if it had been used to avoid using on other dongles.
> >>>
> >>> Currently builtin r8152 on Dock still can't be identified.
> >>> First detected r8152 will use the MAC passthrough address.
> >>>
> >>> Signed-off-by: Aaron Ma <aaron.ma@...onical.com>
> >>> ---
> >>>   drivers/net/usb/r8152.c | 10 ++++++++++
> >>>   1 file changed, 10 insertions(+)
> >>>
> >>> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> >>> index f9877a3e83ac..77f11b3f847b 100644
> >>> --- a/drivers/net/usb/r8152.c
> >>> +++ b/drivers/net/usb/r8152.c
> >>> @@ -1605,6 +1605,7 @@ static int
> >>> vendor_mac_passthru_addr_read(struct r8152 *tp, struct sockaddr
> >>> *sa) char *mac_obj_name; acpi_object_type mac_obj_type;
> >>>   	int mac_strlen;
> >>> +	struct net_device *ndev;
> >>>   
> >>>   	if (tp->lenovo_macpassthru) {
> >>>   		mac_obj_name = "\\MACA";
> >>> @@ -1662,6 +1663,15 @@ static int
> >>> vendor_mac_passthru_addr_read(struct r8152 *tp, struct sockaddr
> >>> *sa) ret = -EINVAL; goto amacout;
> >>>   	}
> >>> +	rcu_read_lock();
> >>> +	for_each_netdev_rcu(&init_net, ndev) {
> >>> +		if (strncmp(buf, ndev->dev_addr, 6) == 0) {
> >>> +			rcu_read_unlock();
> >>> +			goto amacout;  
> >>
> >> Since the original PCI netdev will always be there, that would
> >> disable inheritance would it not?
> >> I guess a strncmp(MODULE_NAME, info->driver, strlen(MODULE_NAME))
> >> is needed as well.
> >>  
> 
> PCI ethernet could be a builtin one on dock since there will be TBT4
> dock.

In my X280 there is a PCI device in the laptop, always there. And its
MAC is the one found in ACPI. Did not try but i think for such devices
there would never be inheritance even if one wanted and used a Lenovo
dock that is supposed to do it.

Maybe i should try the patch but it seems like it defeats inheritance
completely. Well depending on probe order ...

regards,
Henning


> >> Maybe leave here with
> >> netif_info()
> >>  
> 
> Not good to print in rcu lock.
> 
> >> And move the whole block up, we can skip the whole ACPI story if we
> >> find the MAC busy.  
> > 
> > That is wrong, need to know that MAC so can not move up too much.
> > But maybe above the is_valid_ether_addr  
> 
> The MAC passthough address is read from ACPI.
> ACPI read only happens once during r8152 driver probe.
> To keep the lock less time, do it after is_valid_ether_addr.
> 
> > 
> > Henning
> >   
> >>> +		}
> >>> +	}
> >>> +	rcu_read_unlock();  
> >>
> >> Not sure if this function is guaranteed to only run once at a time,
> >> otherwise i think that is a race. Multiple instances could make it
> >> to this very point at the same time.
> >>  
> 
> Run once for one device.
> So add a safe lock.
> 
> Aaron
> 
> >> Henning
> >>  
> >>>   	memcpy(sa->sa_data, buf, 6);
> >>>   	netif_info(tp, probe, tp->netdev,
> >>>   		   "Using pass-thru MAC addr %pM\n",
> >>> sa->sa_data); 
> >>  
> >