netdev - Re: Fixing CVE-2017-16939 in v4.4.y and possibly v3.18.y

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Date:   Sun, 3 Dec 2017 01:44:08 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Fixing CVE-2017-16939 in v4.4.y and possibly v3.18.y

On Sat, Dec 02, 2017 at 04:20:40PM -0800, Guenter Roeck wrote:
> On 12/01/2017 11:48 AM, Michal Kubecek wrote:
> > On Thu, Nov 30, 2017 at 10:37:40AM -0800, Guenter Roeck wrote:
> > > Hi,
> > > 
> > > The fix for CVE-2017-16939 has been applied to v4.9.y, but not to v4.4.y
> > > and older kernels. However, I confirmed that running the published POC
> > > (see https://blogs.securiteam.com/index.php/archives/3535) does crash a 4.4
> > > kernel.
> > > 
> > > I confirmed that the following two patches fix the problem in v4.4.y.
> > > Please consider applying them to v4.4.y (and possibly v3.18.y).
> > > 
> > > fc9e50f5a5a4e ("netlink: add a start callback for starting a netlink dump")
> > > 1137b5e2529a8 ("ipsec: Fix aborted xfrm policy dump crash")
> > > 
> > > My apologies for the noise if this is already under consideration.
> > 
> > It's a bit too big hammer. As Nicolai Stange noticed when we were
> 
> The hammer is just as big as the upstream hammer. Personally I prefer the
> upstream patch; I don't see a reason to deviate from upstream just because
> the upstream solution is more complex than necessary.

Comparing that little patch with the combination of the two commits,
I would say we have a very different idea what "as big as" means. :-)

> > handling this for SLE12 (where fc9e50f5a5a4e would break kABI), it's
> 
> I didn't know that this is even a concern for stable releases. Is there
> some guideline that kABI changes should be avoided in stable releases ?

Not to my knowledge, stable updates break kABI quite often. I just
mentioned it to explain why we had stronger motivation to find another
solution.

Michal Kubecek