Re: Request for stable 4.14.x inclusion: net: don't call update_pmtu unconditionally

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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@xxxxxxxxx>
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@xxxxxxxx>
CC: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>

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



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