netdev - Re: KASAN: use-after-free Read in rtnetlink_put

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Message-ID: <CAM_iQpURKOMAaPfs9v7FzhqqQPzj71sQD2LS0eU8cuqTML-YoA@mail.gmail.com>
Date:   Tue, 31 Jul 2018 16:03:13 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        syzbot+41f9c04b50ef70c66947@...kaller.appspotmail.com,
        christian.brauner@...ntu.com, David Miller <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Florian Westphal <fw@...len.de>, Jiri Benc <jbenc@...hat.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        LKML <linux-kernel@...r.kernel.org>,
        lucien xin <lucien.xin@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in rtnetlink_put_metrics

On Tue, Jul 31, 2018 at 6:41 AM Sabrina Dubroca <sd@...asysnail.net> wrote:
>
> 2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
> >
> >
> > On 07/31/2018 05:31 AM, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> > > git tree:       net
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > >
> > > Unfortunately, I don't have any reproducer for this crash yet.
> [...]
>
> > Probably also caused by :
> >
> >
> > commit df18b50448fab1dff093731dfd0e25e77e1afcd1
> > Author: Sabrina Dubroca <sd@...asysnail.net>
> > Date:   Mon Jul 30 16:23:10 2018 +0200
> >
> >     net/ipv6: fix metrics leak
>
> Yeah, I'm looking into both those reports :/

Looks like this commit is completely unnecessary,
fib6_drop_pcpu_from() calls fib6_info_release()
which calls fib6_info_destroy_rcu(), so this metrics
will be released twice...