linux-kernel - Re: [PATCH V2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check

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Date: Wed, 3 Jan 2024 17:19:55 +0800
From: Yuxuan-Hu <20373622@...a.edu.cn>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
 linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
 baijiaju1990@...il.com, sy2239101@...a.edu.cn, buaazhr@...a.edu.cn
Subject: Re: [PATCH V2] Bluetooth: rfcomm: Fix null-ptr-deref in
 rfcomm_check_security

Hi Paul,


Thank you for your kind reply.

I have made the changes you mentioned and submitted a new version of the 
patch.

https://patchwork.kernel.org/project/bluetooth/patch/20240103091043.3379363-1-20373622@buaa.edu.cn/

On 2024/1/3 16:44, Paul Menzel wrote:
> Dear Yuxuan,
>
>
> Thank you for your patch.
>
> Am 03.01.24 um 04:14 schrieb Yuxuan Hu:
>> During our fuzz testing of the connection and disconnection process 
>> at the
>> RFCOMM layer,we discovered this bug.By comparing the packetsfrom a 
>> normal
>
> 1.  Please add a space after punctuation like full stops/periods and 
> commas. (There are more occurrences below.)
> 2.  packets from
>
>> connection and disconnection process with the testcase that triggered a
>> KASAN report, we analyzed the cause of this bug as follows:
>
> s/, we/. We/
>
>> 1. In the packets captured during a normal connection, the host sends a
>> `Read Encryption Key Size` type of `HCI_CMD` packet(Command Opcode: 
>> 0x1408)
>
> Please add a space before (.
>
>> to the controller to inquire the length of encryption key.After 
>> receiving
>> this packet, the controller immediately replies with a Command Complete
>> packet (Event Code: 0x0e) to return the Encryption Key Size.
>>
>> 2. In our fuzz test case, the timing of the controller's response to 
>> this
>> packet was delayed to an unexpected point: after the RFCOMM and L2CAP
>> layers had disconnected but before the HCI layer had disconnected.
>>
>> 3. After receiving the Encryption Key Size Response at the time 
>> described
>> in point 2, the host still called the rfcomm_check_security function.
>> However, by this time `struct l2cap_conn *conn = 
>> l2cap_pi(sk)->chan->conn;`
>> had already been released, and when the function executed
>> `return hci_conn_security(conn->hcon, d->sec_level, auth_type, 
>> d->out);`,
>> specifically when accessing `conn->hcon`, a null-ptr-deref error 
>> occurred.
>>
>> To fix this bug, check if `sk->sk_state` is BT_CLOSED before calling
>> rfcomm_recv_frame in rfcomm_process_rx.
>
> Is this bug covered by a test case already?


Yes, I have submitted this bug in bugzilla include KASAN details and a 
coverable test case.

Here is the link of it:

https://bugzilla.kernel.org/show_bug.cgi?id=218323


>
>> Signed-off-by: Yuxuan Hu <20373622@...a.edu.cn>
>> ---
>> V1 -> V2: Removed the direct check for `conn` being null in 
>> rfcomm_check_security
>>
>>   net/bluetooth/rfcomm/core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
>> index 053ef8f25fae..1d34d8497033 100644
>> --- a/net/bluetooth/rfcomm/core.c
>> +++ b/net/bluetooth/rfcomm/core.c
>> @@ -1941,7 +1941,7 @@ static struct rfcomm_session 
>> *rfcomm_process_rx(struct rfcomm_session *s)
>>       /* Get data directly from socket receive queue without copying 
>> it. */
>>       while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
>>           skb_orphan(skb);
>> -        if (!skb_linearize(skb)) {
>> +        if (!skb_linearize(skb) && sk->sk_state != BT_CLOSED) {
>>               s = rfcomm_recv_frame(s, skb);
>>               if (!s)
>>                   break;
>
> Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>
>
>
> Kind regards,
>
> Paul

Sincerely,

Yuxuan