linux-kernel - Re: [syzbot] KASAN: use-after-free Write in sco_sock

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Message-ID: <33d6d22f-7666-bc08-f626-3821cac9f174@gmail.com>
Date:   Mon, 30 Aug 2021 12:41:48 +0800
From:   Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+2bef95d3ab4daa10155b@...kaller.appspotmail.com>,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        luiz.von.dentz@...el.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout

On 30/8/21 8:15 am, Hillf Danton wrote:
> On Mon, 30 Aug 2021 02:34:11 +0800 Desmond Cheong Zhi Xi wrote:
>>
>> 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?
> 
> LGTM regardless of the uaf reported.
> 
> Hillf

Thanks for taking a look. It passed the Syzbot reproducer too, so I 
think the root cause should have been addressed.

I'll write up a patch to summarize what we found out. May I include you 
as a Co-developed-by: author?

>>
>> #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);
>>   
>>