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

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Date:   Wed, 30 Jan 2019 15:09:19 -0800
From:   Ivan Babrou <ivan@...udflare.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        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

Eric,

Are you going to propose the change then?

I'm happy to test it out.

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
>