From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: Hillf Danton <hdanton@sina.com>,
syzbot <syzbot+2bef95d3ab4daa10155b@syzkaller.appspotmail.com>
Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org,
luiz.von.dentz@intel.com, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout
Date: Mon, 30 Aug 2021 02:34:11 +0800 [thread overview]
Message-ID: <9b1afb1f-45d5-8664-eeb6-e8373d95cad3@gmail.com> (raw)
In-Reply-To: <11a30bc1-574f-aa1a-21d6-b886de9fc981@gmail.com>
On 29/8/21 10:53 pm, Desmond Cheong Zhi Xi wrote:
> 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.
>
Ok I went back to make a more thorough audit. Even without calling
cancel_delayed_work_sync, sco_sock_timeout should not cause a UAF.
I believe the real issue is that we can allocate a connection twice in
sco_connect. This means that the first connection gets lost and we're
unable to clean it up properly.
Thoughts on this?
#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
@@ -578,9 +578,6 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
addr->sa_family != AF_BLUETOOTH)
return -EINVAL;
- if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
- return -EBADFD;
-
if (sk->sk_type != SOCK_SEQPACKET)
return -EINVAL;
@@ -591,6 +588,13 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
lock_sock(sk);
+ if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+ hci_dev_unlock(hdev);
+ hci_dev_put(hdev);
+ err = -EBADFD;
+ goto done;
+ }
+
/* Set destination address and psm */
bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);
next prev parent reply other threads:[~2021-08-29 18:34 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
2021-08-29 18:34 ` Desmond Cheong Zhi Xi [this message]
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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