Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

Commit Message

Yuxuan Hu Dec. 26, 2023, 7:43 a.m. UTC

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.

Adding a check for whether `conn` is a null pointer to fix this bug.

Signed-off-by: Yuxuan Hu <[e-mail]>
---
 net/bluetooth/rfcomm/core.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

[e-mail] Dec. 26, 2023, 8:35 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=812867

---Test result---

Test Summary:
CheckPatch                    PASS      1.56 seconds
GitLint                       PASS      0.50 seconds
SubjectPrefix                 PASS      0.19 seconds
BuildKernel                   PASS      27.98 seconds
CheckAllWarning               PASS      30.69 seconds
CheckSparse                   PASS      36.00 seconds
CheckSmatch                   PASS      99.34 seconds
BuildKernel32                 PASS      27.17 seconds
TestRunnerSetup               PASS      432.08 seconds
TestRunner_l2cap-tester       PASS      22.88 seconds
TestRunner_iso-tester         PASS      47.44 seconds
TestRunner_bnep-tester        PASS      6.75 seconds
TestRunner_mgmt-tester        PASS      158.34 seconds
TestRunner_rfcomm-tester      PASS      10.73 seconds
TestRunner_sco-tester         PASS      14.20 seconds
TestRunner_ioctl-tester       PASS      11.96 seconds
TestRunner_mesh-tester        PASS      8.70 seconds
TestRunner_smp-tester         PASS      9.57 seconds
TestRunner_userchan-tester    PASS      7.16 seconds
IncrementalBuild              PASS      26.35 seconds



---
Regards,
Linux Bluetooth

Patch

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 053ef8f25fae..5ffa197fdb48 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -228,6 +228,9 @@  static int rfcomm_check_security(struct rfcomm_dlc *d)
 		auth_type = HCI_AT_NO_BONDING;
 		break;
 	}
+
+	if (!conn)
+		return 0;
 
 	return hci_conn_security(conn->hcon, d->sec_level, auth_type,
 				 d->out);