From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: Hillf Danton <hdanton@sina.com>
Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org,
luiz.von.dentz@intel.com,
syzbot <syzbot+2bef95d3ab4daa10155b@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout
Date: Sun, 29 Aug 2021 22:53:10 +0800 [thread overview]
Message-ID: <11a30bc1-574f-aa1a-21d6-b886de9fc981@gmail.com> (raw)
In-Reply-To: <20210829082929.2897-1-hdanton@sina.com>
On 29/8/21 4:29 pm, Hillf Danton wrote:
> On Fri, 27 Aug 2021 15:58:34 +0800 Desmond Cheong Zhi Xi wrote:
>> On 27/8/21 9:19 am, Hillf Danton wrote:
>>> On Thu, 26 Aug 2021 09:29:24 -0700
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit: e3f30ab28ac8 Merge branch 'pktgen-samples-next'
>>>> git tree: net-next
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13249c96300000
>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=ef482942966bf763
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=2bef95d3ab4daa10155b
>>>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a29ea9300000
>>>>
>>>> The issue was bisected to:
>>>>
>>>> commit e1dee2c1de2b4dd00eb44004a4bda6326ed07b59
>>>> Author: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>>>> Date: Tue Aug 10 04:14:10 2021 +0000
>>>>
>>>> Bluetooth: fix repeated calls to sco_sock_kill
>
> To fix the uaf, grab another hold to sock to make the timeout work safe.
>
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git e3f30ab28ac8
>
> --- a/net/bluetooth/sco.c
> +++ b/net/bluetooth/sco.c
> @@ -190,15 +190,14 @@ static void sco_conn_del(struct hci_conn
> sco_conn_unlock(conn);
>
> if (sk) {
> - sock_hold(sk);
> lock_sock(sk);
> sco_sock_clear_timer(sk);
> sco_chan_del(sk, err);
> release_sock(sk);
> - sock_put(sk);
>
> /* Ensure no more work items will run before freeing conn. */
> cancel_delayed_work_sync(&conn->timeout_work);
> + sock_put(sk);
Hi Hillf,
Saw that this passed the reproducer. But on closer inspection, I think
what's happening is that sco_conn_del is never run.
So the extra sock_hold prevents a UAF, but that's because now the
reference count never goes to 0. In my opinion, something closer to your
previous proposal (+ also addressing other calls to __sco_sock_close)
where we call cancel_delayed_work_sync after the channel is deleted
would address the root cause better.
Just my two cents.
> }
>
> hcon->sco_data = NULL;
> @@ -212,6 +211,8 @@ static void __sco_chan_add(struct sco_co
>
> sco_pi(sk)->conn = conn;
> conn->sk = sk;
> + /* make timeout_work safe; will be put in sco_conn_del() */
> + sock_hold(sk);
>
> INIT_DELAYED_WORK(&conn->timeout_work, sco_sock_timeout);
>
> --
>
next prev parent reply other threads:[~2021-08-29 14:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-26 16:29 [syzbot] KASAN: use-after-free Write in sco_sock_timeout syzbot
[not found] ` <20210827011931.2323-1-hdanton@sina.com>
2021-08-27 7:58 ` Desmond Cheong Zhi Xi
[not found] ` <20210829082929.2897-1-hdanton@sina.com>
2021-08-29 8:51 ` syzbot
2021-08-29 14:53 ` Desmond Cheong Zhi Xi [this message]
2021-08-29 18:34 ` Desmond Cheong Zhi Xi
2021-08-30 3:50 ` syzbot
[not found] ` <20210830001538.1980-1-hdanton@sina.com>
2021-08-30 4:41 ` Desmond Cheong Zhi Xi
2022-02-23 16:15 ` syzbot
[not found] <20220227025605.2681-1-hdanton@sina.com>
2022-02-27 3:07 ` syzbot
[not found] <20220227032747.2752-1-hdanton@sina.com>
2022-02-27 3:39 ` syzbot
[not found] <20220227060827.2844-1-hdanton@sina.com>
2022-02-27 6:20 ` syzbot
[not found] <20220227074046.2963-1-hdanton@sina.com>
2022-02-27 7:53 ` syzbot
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