[v2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

[PATCH V2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

Posted by Yuxuan Hu 1 year, 11 months ago

During our fuzz testing of the connection and disconnection process at the
RFCOMM layer,we discovered this bug.By comparing the packetsfrom a normal
connection and disconnection process with the testcase that triggered a
KASAN report, we analyzed the cause of this bug as follows:

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)
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.

Signed-off-by: Yuxuan Hu <20373622@buaa.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;
-- 
2.25.1

Re: [PATCH V2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

Posted by Paul Menzel 1 year, 11 months ago

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@buaa.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@molgen.mpg.de>


Kind regards,

Paul

Re: [PATCH V2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

Posted by Yuxuan-Hu 1 year, 11 months ago

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@buaa.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@molgen.mpg.de>
>
>
> Kind regards,
>
> Paul

Sincerely,

Yuxuan