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

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Date:   Wed, 26 Sep 2018 14:44:46 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     syzbot+37b8770e6d5a8220a039@...kaller.appspotmail.com
Cc:     David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in tcf_block_find

On Wed, Sep 26, 2018 at 8:44 AM syzbot
<syzbot+37b8770e6d5a8220a039@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    4b1bd6976945 net: phy: marvell: Fix build.
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16f763fa400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=443816db871edd66
> dashboard link: https://syzkaller.appspot.com/bug?extid=37b8770e6d5a8220a039
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17a5614e400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141a532a400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+37b8770e6d5a8220a039@...kaller.appspotmail.com
>
> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
> 8021q: adding VLAN 0 to HW filter on device team0
> ==================================================================
> BUG: KASAN: use-after-free in tcf_block_find+0x9d1/0xb90
> net/sched/cls_api.c:646
> Read of size 4 at addr ffff8801cc126978 by task syz-executor002/5646
>
> CPU: 1 PID: 5646 Comm: syz-executor002 Not tainted 4.19.0-rc5+ #232
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
>   print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
>   kasan_report_error mm/kasan/report.c:354 [inline]
>   kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
>   __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
>   tcf_block_find+0x9d1/0xb90 net/sched/cls_api.c:646

Hmm. looks like missing a rcu_dereference() here:

                if (!*parent) {
                        *q = dev->qdisc;
                        *parent = (*q)->handle;