netdev - Re: BUG: KASAN: double-free or invalid-free in ip

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Message-ID: <CANn89iJ_LOc+yPtyQrRQieniy5Pga=CVKorO4qdvHXCqKgyaHw@mail.gmail.com>
Date:   Wed, 30 Jan 2019 15:13:32 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ivan Babrou <ivan@...udflare.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Michal Kubecek <mkubecek@...e.cz>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Ignat Korchagin <ignat@...udflare.com>,
        Shawn Bohrer <sbohrer@...udflare.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: BUG: KASAN: double-free or invalid-free in ip_defrag after
 upgrade from 4.19.13

On Wed, Jan 30, 2019 at 3:09 PM Ivan Babrou <ivan@...udflare.com> wrote:
>
> Eric,
>
> Are you going to propose the change then?
>
> I'm happy to test it out.
>

This is indeed a bug in linux stable tree only.

The err=-EINVAL move was part of a patch that was not backported
(since it was not a bug fix)

commit 0ff89efb524631ac9901b81446b453c29711c376
Author: Peter Oskolkov <posk@...gle.com>
Date:   Tue Aug 28 11:36:19 2018 -0700

    ip: fail fast on IP defrag errors


> On Wed, Jan 30, 2019 at 3:00 PM Michal Kubecek <mkubecek@...e.cz> wrote:
> >
> > On Wed, Jan 30, 2019 at 02:26:32PM -0800, Ivan Babrou wrote:
> > > Hey,
> > >
> > > Continuing from this thread earlier today:
> > >
> > > * https://marc.info/?t=154886729100001&r=1&w=2
> > >
> > > We fired up KASAN enabled kernel one one of those machine and this is
> > > what we saw:
> > ...
> > > This commit from 4.19.14 seems relevant:
> > >
> > > * https://github.com/torvalds/linux/commit/d5f9565c8d5ad3cf94982223cfcef1169b0bb60f
> > >
> > > As a reminder, we upgraded from 4.19.13 and started seeing crashes.
> >
> > Unfortunately I'm on vacation this week so that my capability to look
> > deeper into this is limited but there seems to be one obvious problem
> > with the 4.19.y backport: in mainline, there is
> >
> >         err = -EINVAL;
> >
> > right on top of the "Find out where to put this fragment." comment which
> > had been added by commit 0ff89efb5246 ("ip: fail fast on IP defrag
> > errors"). In 4.19.y backport of the commit, this assignment is missing
> > so that the value of err at this point comes from earlier
> > pskb_trim_rcsum() call so that it must be zero and if we take any of the
> > "goto err" added by commit d5f9565c8d5a, we drop the packet by calling
> > kfree_skb() but return zero so that caller doesn't know about it.
> >
> > Michal Kubecek
> >