netdev - RE: netdev carrier changes is one even after ethernet link up.

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:   Fri, 1 Sep 2017 05:41:00 +0000
From:   Bhadram Varka <vbhadram@...dia.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>
CC:     linux-netdev <netdev@...r.kernel.org>
Subject: RE: netdev carrier changes is one even after ethernet link up.

Thanks for responding.

-----Original Message-----
From: Florian Fainelli [mailto:f.fainelli@...il.com] 
Sent: Friday, September 01, 2017 5:53 AM
To: Bhadram Varka <vbhadram@...dia.com>; andrew@...n.ch
Cc: linux-netdev <netdev@...r.kernel.org>
Subject: Re: netdev carrier changes is one even after ethernet link up.

On 08/30/2017 10:53 PM, Bhadram Varka wrote:
> Hi,
> 
>  
> 
> I have observed that carrier_changes is one even in case of the 
> ethernet link is up.
> 
>  
> 
> After investigating the code below is my observation –
> 
>  
> 
> ethernet_driver_probe()
> 
> +--->phy_connect()
> 
> |     +--->phy_attach_direct()
> 
> |           +---> netif_carrier_off()    : which increments
> carrier_changes to one.
> 
> +--->register_netdevice() : will the carrier_changes becomes zero here ?
> 
> +--->netif_carrier_off(): not increment the carrier_changes since
> __LINK_STATE_NOCARRIER already set.
> 
>  
> 
> From ethernet driver open will start the PHY and trigger the 
> phy_state_machine.
> 
> Phy_state_machine workqueue calling netif_carrier_on() once the link is UP.
> 
> netif_carrier_on() increments the carrier_changes by one.

If the call trace is correct, then there is at least two problems here:

- phy_connect() does start the PHY machine which means that as soon as it detects a link state of any kind (up or down) it can call
netif_carrier_off() respectively netif_carrier_on()

- as soon as you call register_netdevice() notifiers run and other parts of the kernel or user-space programs can see an inconsistent link state

I would suggest doing the following sequence instead:

netif_carrier_off()
register_netdevice()
phy_connect()

Which should result in a consistent link state and carrier value.

Yes, It will address the issue. 

If we did the phy_conect in ndo_open it will make the carrier changes as one. But if we did in probe function then it's not working.

In ethernet driver probe - (below sequence is not working)
phy_connect()
register_netdevice()
netif_carrier_off()

working sequence:
In probe():
register_netdevice()
ndo_open:
           phy_connect()

Thanks,
Bhadram.
> 
>  
> 
> After link is UP if we check the carrier_changes sysfs node - it will 
> be one only.
> 
>  
> 
> $ cat /sys/class/net/eth0/carrier_changes
> 
> 1
> 
>  
> 
> After reverting the change - https://lkml.org/lkml/2016/1/9/173 (net:
> phy: turn carrier off on phy attach) then I could see the carrier 
> changes incremented to 2 after Link UP.
> 
> $ cat /sys/class/net/eth0/carrier_changes
> 
> 2
> 
>  
> 
> Thanks,
> 
> Bhadram.
> 
> ----------------------------------------------------------------------
> -- This email message is for the sole use of the intended recipient(s) 
> and may contain confidential information.  Any unauthorized review, 
> use, disclosure or distribution is prohibited.  If you are not the 
> intended recipient, please contact the sender by reply email and 
> destroy all copies of the original message.
> ----------------------------------------------------------------------
> --


--
Florian