linux-kernel - Re: KASAN: use-after-free Read in rtnetlink_put

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Message-ID: <CAM_iQpUN=1-b13OfHcuahPGw6kDMBhFHAqu70NJ7UvmQreM6LQ@mail.gmail.com>
Date:   Wed, 1 Aug 2018 22:23:42 -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 <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 Wed, Aug 1, 2018 at 1:15 AM Sabrina Dubroca <sd@...asysnail.net> wrote:
>
> 2018-07-31, 16:03:13 -0700, Cong Wang wrote:
> > 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...
>
> kmemleak disagrees:


This information is missing from changelog. :)


>
> unreferenced object 0xffff88006b605080 (size 96):
>   comm "ip", pid 433, jiffies 4294889793 (age 74.844s)
>   hex dump (first 32 bytes):
>     00 00 00 00 f4 01 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<000000002650e4e2>] ip6_route_info_create+0x770/0x4050
>     [<000000000a8d4c52>] ip6_route_add+0x18/0x90
>     [<00000000474d669c>] inet6_rtm_newroute+0xeb/0x100
>     [<0000000019fb732d>] rtnetlink_rcv_msg+0x3b5/0xb40
>     [<000000006f891e19>] netlink_rcv_skb+0x137/0x380
>     [<0000000070451985>] netlink_unicast+0x47f/0x6e0
>     [<000000004487d656>] netlink_sendmsg+0x7a7/0x10c0
>     [<0000000089fdf5ae>] sock_sendmsg+0xac/0x160
>     [<00000000aae19c54>] ___sys_sendmsg+0x6e0/0xbb0
>     [<00000000a3906352>] __sys_sendmsg+0xdc/0x230
>     [<00000000c7c8548a>] do_syscall_64+0x15d/0x740
>     [<000000007dfdad73>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>     [<000000003adb705a>] 0xffffffffffffffff

My kernel dev machine is broken now.
I will take a look tomorrow after I fix my kernel dev machine.

Thanks!