[V3] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

Commit Message

Yuxuan Hu Jan. 3, 2024, 9:10 a.m. UTC

During our fuzz testing of the connection and disconnection process at the
RFCOMM layer, we discovered this bug. By comparing the packets from 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 Completepacket (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 <[e-mail]>
---
V1 -> V2: Check earlier on rfcomm_process_rx
V2 -> V3: Fixed formatting errors in the commit

 net/bluetooth/rfcomm/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

[e-mail] Jan. 3, 2024, 9:33 a.m. UTC | #1

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=814026

---Test result---

Test Summary:
CheckPatch                    PASS      1.48 seconds
GitLint                       PASS      0.25 seconds
SubjectPrefix                 PASS      0.07 seconds
BuildKernel                   PASS      27.35 seconds
CheckAllWarning               PASS      30.21 seconds
CheckSparse                   PASS      35.87 seconds
CheckSmatch                   PASS      98.79 seconds
BuildKernel32                 PASS      26.56 seconds
TestRunnerSetup               PASS      428.00 seconds
TestRunner_l2cap-tester       PASS      22.86 seconds
TestRunner_iso-tester         PASS      44.57 seconds
TestRunner_bnep-tester        PASS      6.83 seconds
TestRunner_mgmt-tester        PASS      161.35 seconds
TestRunner_rfcomm-tester      PASS      10.88 seconds
TestRunner_sco-tester         PASS      14.36 seconds
TestRunner_ioctl-tester       PASS      11.83 seconds
TestRunner_mesh-tester        PASS      8.58 seconds
TestRunner_smp-tester         PASS      9.62 seconds
TestRunner_userchan-tester    PASS      7.58 seconds
IncrementalBuild              PASS      25.43 seconds



---
Regards,
Linux Bluetooth

[e-mail] Jan. 8, 2024, 6 p.m. UTC | #2

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <[e-mail]>:

On Wed,  3 Jan 2024 17:10:43 +0800 you wrote:
> During our fuzz testing of the connection and disconnection process at the
> RFCOMM layer, we discovered this bug. By comparing the packets from 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 Completepacket (Event Code: 0x0e) to return the
> Encryption Key Size.
> 
> [...]

Here is the summary with links:
  - [V3] Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security
    https://git.kernel.org/bluetooth/bluetooth-next/c/6ec00b0737fe

You are awesome, thank you!

Patch

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;