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Date:   Wed, 6 Dec 2017 13:50:04 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Tejun Heo <tj@...nel.org>,
        syzbot 
        <bot+ea75c0ffcd353d32515f064aaebefc5279e6161e@...kaller.appspotmail.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        David Miller <davem@...emloft.net>, tom@...ntonium.net,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: KASAN: use-after-free Read in get_work_pool

On Fri, Oct 27, 2017 at 11:18 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Thu, Oct 26, 2017 at 11:00 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> On Thu, Oct 26, 2017 at 7:58 PM, Tejun Heo <tj@...nel.org> wrote:
>>> Hello,
>>>
>>> On Thu, Oct 26, 2017 at 09:35:44AM -0700, syzbot wrote:
>>>> BUG: KASAN: use-after-free in __read_once_size
>>>> include/linux/compiler.h:276 [inline]
>>>> BUG: KASAN: use-after-free in atomic64_read
>>>> arch/x86/include/asm/atomic64_64.h:21 [inline]
>>>> BUG: KASAN: use-after-free in atomic_long_read
>>>> include/asm-generic/atomic-long.h:44 [inline]
>>>> BUG: KASAN: use-after-free in get_work_pool+0x1c2/0x1e0
>>>> kernel/workqueue.c:709
>>>> Read of size 8 at addr ffff8801cc58c378 by task syz-executor5/21326
>>>>
>>>> CPU: 1 PID: 21326 Comm: syz-executor5 Not tainted 4.13.0+ #43
>>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>>> BIOS Google 01/01/2011
>>>> Call Trace:
>>>>  __dump_stack lib/dump_stack.c:16 [inline]
>>>>  dump_stack+0x194/0x257 lib/dump_stack.c:52
>>>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>>>  kasan_report+0x24e/0x340 mm/kasan/report.c:409
>>>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>>>  __read_once_size include/linux/compiler.h:276 [inline]
>>>>  atomic64_read arch/x86/include/asm/atomic64_64.h:21 [inline]
>>>>  atomic_long_read include/asm-generic/atomic-long.h:44 [inline]
>>>>  get_work_pool+0x1c2/0x1e0 kernel/workqueue.c:709
>>>>  __queue_work+0x235/0x1150 kernel/workqueue.c:1401
>>>>  queue_work_on+0x16a/0x1c0 kernel/workqueue.c:1486
>>>>  queue_work include/linux/workqueue.h:489 [inline]
>>>>  strp_check_rcv+0x25/0x30 net/strparser/strparser.c:553
>>>>  kcm_attach net/kcm/kcmsock.c:1439 [inline]
>>>>  kcm_attach_ioctl net/kcm/kcmsock.c:1460 [inline]
>>>>  kcm_ioctl+0x826/0x1610 net/kcm/kcmsock.c:1695
>>>>  sock_do_ioctl+0x65/0xb0 net/socket.c:961
>>>>  sock_ioctl+0x2c2/0x440 net/socket.c:1058
>>>>  vfs_ioctl fs/ioctl.c:45 [inline]
>>>>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
>>>>  SYSC_ioctl fs/ioctl.c:700 [inline]
>>>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>>>>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>>>
>>> Looks like kcm is trying to reuse a work item whose last workqueue has
>>> been destroyed without re-initing it.  A work item needs to be
>>> reinit'd.
>>
>> +kcm maintainers
>
> Can you try the fix below? There is no C reproducer so I can't verify it.


Hi Cong,

syzbot can now test proposed patches, see
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#communication-with-syzbot
for details. Please give it a try.

> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
> index af4e76ac88ff..7816f44c576a 100644
> --- a/net/kcm/kcmsock.c
> +++ b/net/kcm/kcmsock.c
> @@ -1433,11 +1433,12 @@ static int kcm_attach(struct socket *sock,
> struct socket *csock,
>         KCM_STATS_INCR(mux->stats.psock_attach);
>         mux->psocks_cnt++;
>         psock_now_avail(psock);
> -       spin_unlock_bh(&mux->lock);
>
>         /* Schedule RX work in case there are already bytes queued */
>         strp_check_rcv(&psock->strp);
>
> +       spin_unlock_bh(&mux->lock);
> +
>         return 0;
>  }

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