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

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Message-ID: <d30e0344-d753-4fa5-9308-5b344c585495@molgen.mpg.de>
Date: Wed, 3 Jan 2024 09:44:48 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Yuxuan Hu <20373622@...a.edu.cn>
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

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?

> 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