netdev - Re: [Intel-wired-lan] [PATCH] igc: fix a log entry using uninitialized netdev

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Message-ID: <87r0etwa9p.fsf@intel.com>
Date: Thu, 25 Apr 2024 11:46:26 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Corinna Vinschen <vinschen@...hat.com>
Cc: Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org
Subject: Re: [Intel-wired-lan] [PATCH] igc: fix a log entry using
 uninitialized netdev

Corinna Vinschen <vinschen@...hat.com> writes:

> On Apr 24 17:06, Vinicius Costa Gomes wrote:
>> Andrew Lunn <andrew@...n.ch> writes:
>> 
>> > On Tue, Apr 23, 2024 at 12:24:54PM +0200, Corinna Vinschen wrote:
>> >> During successful probe, igc logs this:
>> >> 
>> >> [    5.133667] igc 0000:01:00.0 (unnamed net_device) (uninitialized): PHC added
>> >>                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> >> The reason is that igc_ptp_init() is called very early, even before
>> >> register_netdev() has been called. So the netdev_info() call works
>> >> on a partially uninitialized netdev.
>> >> 
>> >> Fix this by calling igc_ptp_init() after register_netdev(), right
>> >> after the media autosense check, just as in igb.  Add a comment,
>> >> just as in igb.
>> >
>> > The network stack can start sending and receiving packet before
>> > register_netdev() returns. This is typical of NFS root for example. Is
>> > there anything in igc_ptp_init() which could cause such packet
>> > transfers to explode?
>> >
>> 
>> There might be a very narrow window (probably impossible?), what I can
>> see is:
>> 
>> 1. the netdevice is exposed to userspace;
>> 2. userspace does the SIOCSHWTSTAMP ioctl() to enable TX timestamps;
>> 3. userspace sends a packet that is going to be timestamped;
>> 
>> if this happens before igc_ptp_init() is called, adapter->ptp_tx_lock is
>> going to be uninitialized, and (3) is going to crash.
>
> The same would then be possible on igb as well, wouldn't it?
>

Given how many years igb is being used, perhaps "possible" is too strong
:-)

On igb what exists is slightly different, as there's no ptp_tx_lock
there, the "problem" there is trying to enqueue a job on a workqueue
that is going to be uninitialized, during this time window.

And to be sure, I am still uncertain that this is possible.

>
>> If there's anything that makes this impossible/extremely unlikely, the
>> patch looks good:
>> 
>> Acked-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>> 
>> 
>> Cheers,
>> -- 
>> Vinicius
>
>
> Corinna
>

Cheers,
-- 
Vinicius