[PATCH v2] Bluetooth: l2cap: Process valid commands in too long frame

["Frédéric Danis" <frederic.danis@collabora.com>]

This is required for passing PTS test cases:
- L2CAP/COS/CED/BI-14-C
  Multiple Signaling Command in one PDU, Data Truncated, BR/EDR,
  Connection Request
- L2CAP/COS/CED/BI-15-C
  Multiple Signaling Command in one PDU, Data Truncated, BR/EDR,
  Disconnection Request

The test procedure defined in L2CAP.TS.p39 for both tests is:
1. The Lower Tester sends a C-frame to the IUT with PDU Length set
   to 8 and Channel ID set to the correct signaling channel for the
   logical link. The Information payload contains one L2CAP_ECHO_REQ
   packet with Data Length set to 0 with 0 octets of echo data and
   one command packet and Data Length set as specified in Table 4.6
   and the correct command data.
2. The IUT sends an L2CAP_ECHO_RSP PDU to the Lower Tester.
3. Perform alternative 3A, 3B, 3C, or 3D depending on the IUT’s
   response.
   Alternative 3A (IUT terminates the link):
     3A.1 The IUT terminates the link.
     3A.2 The test ends with a Pass verdict.
   Alternative 3B (IUT discards the frame):
     3B.1 The IUT does not send a reply to the Lower Tester.
   Alternative 3C (IUT rejects PDU):
     3C.1 The IUT sends an L2CAP_COMMAND_REJECT_RSP PDU to the
          Lower Tester.
   Alternative 3D (Any other IUT response):
     3D.1 The Upper Tester issues a warning and the test ends.
4. The Lower Tester sends a C-frame to the IUT with PDU Length set
   to 4 and Channel ID set to the correct signaling channel for the
   logical link. The Information payload contains Data Length set to
   0 with an L2CAP_ECHO_REQ packet with 0 octets of echo data.
5. The IUT sends an L2CAP_ECHO_RSP PDU to the Lower Tester.

With expected outcome:
  In Steps 2 and 5, the IUT responds with an L2CAP_ECHO_RSP.
  In Step 3A.1, the IUT terminates the link.
  In Step 3B.1, the IUT does not send a reply to the Lower Tester.
  In Step 3C.1, the IUT rejects the PDU.
  In Step 3D.1, the IUT sends any valid response.

Currently PTS fails with the following logs:
  Failed to receive ECHO RESPONSE.

And HCI logs:
> ACL Data RX: Handle 11 flags 0x02 dlen 20
      L2CAP: Information Response (0x0b) ident 2 len 12
        Type: Fixed channels supported (0x0003)
        Result: Success (0x0000)
        Channels: 0x000000000000002e
          L2CAP Signaling (BR/EDR)
          Connectionless reception
          AMP Manager Protocol
          L2CAP Signaling (LE)
> ACL Data RX: Handle 11 flags 0x02 dlen 13
        frame too long
        08 01 00 00 08 02 01 00 aa                       .........

Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>
---
v1->v2: Enhance comment with PTS test cases description

 net/bluetooth/l2cap_core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index f1c4b8bd7a8b..1bba7152fd70 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -7539,6 +7539,22 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
 		if (skb->len > len) {
 			BT_ERR("Frame is too long (len %u, expected len %d)",
 			       skb->len, len);
+			/* PTS test cases L2CAP/COS/CED/BI-14-C and BI-15-C
+			 * (Multiple Signaling Command in one PDU, Data
+			 * Truncated, BR/EDR) send a C-frame to the IUT with
+			 * PDU Length set to 8 and Channel ID set to the
+			 * correct signaling channel for the logical link.
+			 * The Information payload contains one L2CAP_ECHO_REQ
+			 * packet with Data Length set to 0 with 0 octets of
+			 * echo data and one invalid command packet due to
+			 * data truncated in PDU but present in HCI packet.
+			 *
+			 * Shorter the socket buffer to the PDU length to
+			 * allow to process valid commands from the PDU before
+			 * setting the socket unreliable.
+			 */
+			skb->len = len;
+			l2cap_recv_frame(conn, skb);
 			l2cap_conn_unreliable(conn, ECOMM);
 			goto drop;
 		}
-- 
2.43.0