netdev - Re: Request for stable 4.14.x inclusion: net: don't call update

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Message-ID: <ae1401af-a400-f6de-658e-bae0b29c52e4@ehuk.net>
Date:   Fri, 27 Apr 2018 17:04:30 +0100
From:   Eddie Chapman <eddie@...k.net>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Thomas Deutschmann <whissi@...too.org>
Cc:     stable@...r.kernel.org, davem@...emloft.net,
        nicolas.dichtel@...nd.com, netdev@...r.kernel.org
Subject: Re: Request for stable 4.14.x inclusion: net: don't call update_pmtu
 unconditionally

On 27/04/18 15:45, Greg KH wrote:
> On Fri, Apr 27, 2018 at 03:51:25PM +0200, Greg KH wrote:
>> On Fri, Apr 27, 2018 at 02:20:07PM +0200, Thomas Deutschmann wrote:
>>> On 2018-04-22 23:50, Thomas Deutschmann wrote:
>>>> Hi,
>>>>
>>>> please add
>>>>
>>>>>  From f15ca723c1ebe6c1a06bc95fda6b62cd87b44559 Mon Sep 17 00:00:00 2001
>>>>> From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>>>>> Date: Thu, 25 Jan 2018 19:03:03 +0100
>>>>> Subject: net: don't call update_pmtu unconditionally
>>>>>
>>>>> Some dst_ops (e.g. md_dst_ops)) doesn't set this handler. It may result to:
>>>>> "BUG: unable to handle kernel NULL pointer dereference at           (null)"
>>>>>
>>>>> Let's add a helper to check if update_pmtu is available before calling it.
>>>>>
>>>>> Fixes: 52a589d51f10 ("geneve: update skb dst pmtu on tx path")
>>>>> Fixes: a93bf0ff4490 ("vxlan: update skb dst pmtu on tx path")
>>>>> CC: Roman Kapl <code@...pl.cz>
>>>>> CC: Xin Long <lucien.xin@...il.com>
>>>>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>>>>> Signed-off-by: David S. Miller <davem@...emloft.net>
>>>>
>>>> to 4.14.x.
>>>>
>>>> This fixes NULL derefs caused by a93bf0ff4490 ("vxlan: update
>>>> skb dst pmtu on tx path"), which was backported to 4.14.24.
>>>
>>> *ping* - Not yet applied and not yet queued. Is there a problem with the
>>> patch which prevents a cherry-pick for 4.14.x?
>>
>> This looks like an "obvious" fix for me to pick up.
> 
> Well, it would be "obvious" if it actually applied to the 4.14.y tree :(
> 
> Thomas, did you try this patch out?  I can't apply it as-is, it will
> need a backport.  Please work on that, and test it out, as I don't get
> the impression that you did that here.
> 
> Then post the working backport and I'll be glad to consider it for
> future 4.14.y releases.
> 
> thanks,
> 
> greg k-h
> 

Hi Greg,

I just applied coreos' 4.14 backport of this to your 4.14.38-rc1, which 
booted and is running with no problem:

https://github.com/coreos/linux/commit/f5f2102a531988e24f19a13fdc5b8206007aaad5

AFAIK their backport is already in a coreos release so has received testing.

Comparing their backport to the original, I can see they just needed to 
make the same trivial change to each hunk to make it apply on 4.14.

The backport is linked from this bug report, which is I believe what led 
to the backport being requested here in the first place:
https://github.com/coreos/bugs/issues/2382

Up to you of course if you trust it, just posting in case it helps.

Eddie