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

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(-)

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=813991

---Test result---

Test Summary:
CheckPatch                    PASS      0.62 seconds
GitLint                       FAIL      0.53 seconds
SubjectPrefix                 PASS      0.13 seconds
BuildKernel                   PASS      28.06 seconds
CheckAllWarning               PASS      30.63 seconds
CheckSparse                   PASS      36.02 seconds
CheckSmatch                   PASS      99.18 seconds
BuildKernel32                 PASS      27.78 seconds
TestRunnerSetup               PASS      435.47 seconds
TestRunner_l2cap-tester       PASS      22.88 seconds
TestRunner_iso-tester         PASS      47.18 seconds
TestRunner_bnep-tester        PASS      6.86 seconds
TestRunner_mgmt-tester        PASS      159.08 seconds
TestRunner_rfcomm-tester      PASS      10.80 seconds
TestRunner_sco-tester         PASS      14.49 seconds
TestRunner_ioctl-tester       PASS      12.05 seconds
TestRunner_mesh-tester        PASS      8.67 seconds
TestRunner_smp-tester         PASS      10.14 seconds
TestRunner_userchan-tester    PASS      7.25 seconds
IncrementalBuild              PASS      26.16 seconds

Details
##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
[V2] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
30: B1 Line exceeds max length (81>80): "V1 -> V2: Removed the direct check for `conn` being null in rfcomm_check_security"


---
Regards,
Linux Bluetooth

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