BT_HCI_ERR_INSUFFICIENT_SECURITY during re-discovery

[muli]

Note. This issue only occurs if using the Nordic Soft Device controller or the Packetcraft controller. 

I am working with the nRF5340 audio development boards. 

I have a project with a central device (used as a Broadcast Assistant) and a peripheral device (used as an audio broadcast receiver). They both form an ACL connection and exchange data. 

Whenever the receiver is syncing to a broadcast source and it gets disconnected from the central for whatever reason, the central manages to re-connect to the peripheral, however the BASS discovery fails with BT_HCI_ERR_INSUFFICIENT_SECURITY. The following error is displayed : 

<wrn> bt_gatt: gatt_exchange_mtu_func: conn 0x200018c8 err 0x0e

 . 

The only way to solve this is by rebooting the receiver / peripheral. 

For both the central and receiver applications, bonding is disabled in the proj.conf as follows : 

CONFIG_BT_BONDABLE=n

In that case, I can't understand why the BASS re-discovery would fail due to a security error error.

As mentioned above. This only happens when using the Nordic Soft Device controller or the Packetcraft controller. Using the Zephyr controller, the re-discovery works fine without this security problem. 

How can there be this security issue only when using those two controllers, and by using the Zephyr controller with the exact same configuration (bonding disabled etc.) it is fine?

Below are the logs from my central application when it re-connects. Thanks in advance for any help or suggestions. 

Disconnected from device EE:0B:7C:30:59:12 (random) (reason 0x3e)
About to connect to EE:0B:7C:30:59:12
Connection pending..
Successfully connected to device EE:0B:7C:30:59:12 (random)
Now discovering..
[00:01:04.517,425] <wrn> bt_gatt: gatt_exchange_mtu_func: conn 0x200018c8 err 0x0e
[00:01:04.517,456] <dbg> bt_bap_broadcast_assistant: service_discover_func: Could not discover BASS
Error! BASS discover failed (-6)

    

[Hung Bui]

Hi Paul, 
It's quite strange the MTU exchange would have something to do with security level. 
Could you try to capture a sniffer trace so that it's more clear on why we have that error ? 
Just for clarification, could you point me to where you find that the error was BT_ATT_ERR_AUTHORIZATION?  as far as I know error 0x0e means BT_HCI_ERR_INSUFFICIENT_SECURITY

[muli]

 Hung Bui Here is a sniffer trace from the peripheral / receiver device. This sniffer didn't seem to capture packets when the connection dropped this time . I noticed an LL_TERMINTE_IND during one capture though. 

However, what is the most interesting here I believe are the packets captured during the initial connection from number 4583. There is an Insufficient Authentication error at 4606. It's looking like this is the source of the issue.

What I don't understand though is why the connection still succeeds that first time, and the BASS gets discovered by the central device. Only if the peripheral drops the connection later when it is syncing to an audio broadcast, and the central connects again, BASS discovery fails because of the insufficient security. 

Again this only happens when using either the Packetcraft or Nordic Soft device controller on the central side and not the Zephyr controller (with the exact same application)

How to possibly solve this? Thanks 

capture-peripheral-authentication-issue.pcapng

[ovrebekk]

Hi Paul

I will take over this case from Hung since I have a bit more experience with LE Audio. 

It is interesting that it all works fine when switching to the broadcast_audio_sink application. Have you tried to capture a sniffer trace when everything works, to see if there is some critical difference that can be spotted in the trace? 

I think we should try to reproduce the issue internally so that we can do some tests on our own, speeding up the investigation into the issue. 

Would you be able to share your code so that I can try to reproduce the issue here? 

If you don't want to share your code in a public ticket just let me know, and I will make the ticket private. 

Best regards
Torbjørn

[muli]

Hi ovrebekk . Thanks for looking into this. I haven't actually collected sniffer traces when connected to the broadcast_audio_sink application. I wasn't sure if there is much point. 

What's a real headache is that when I am capturing traces when the problem occurs with the other receiver application, there are no packets indicating what is wrong. We can't see why it disconnected and the re-connection with failed GATT discovery. 

What could be worth trying, to replicate this, is take the existing Nordic audio application as it is, add just add the ability to have an ACL connection from a central device. Connect the central device, keep switching audio broadcasts on the receiver and see that the connection to the central drops at some point.

I can try and share my code next week also. 

Regards,

Paul 

[muli]

Hi ovrebekk 

I've taken the latest Nordic audio application from nrf\applications\nrf5340_audio

I've made some modifications to start advertising if it's a receiver device as follows : 

bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL,0);

and allows a connection from a central device. 

When a central is connected and the receiver is streaming broadcast audio, occasionally the connection drops and I get this error and crash :  

HL [00:01:13.699,676] <inf> bt_mgmt: Disconnected: C2:DA:2D:C3:36:C7 (random) (reason 0x08)
HL [00:01:13.699,707] <wrn> streamctrl_broadcast_sink: Unexpected/unhandled bt_mgmt event: 6
HL [00:01:13.699,707] <err> bt_mgmt_adv: No valid advertising data stored
HL [00:01:13.699,737] <err> bt_mgmt: ERR_CHK Err_code: [-2] @ line: 177
HL [00:01:13.699,737] <err> os: r0/a1:  0x00000003  r1/a2:  0x00000004  r2/a3:  0x00000003
HL [00:01:13.699,737] <err> os: r3/a4:  0x00060591 r12/ip:  0x0000000c r14/lr:  0x0006061b
HL [00:01:13.699,768] <err> os:  xpsr:  0x41100000
HL [00:01:13.699,768] <err> os: s[ 0]:  0x00000000  s[ 1]:  0x00000010  s[ 2]:  0x20017a70  s[ 3]:  0x0006fdd4
HL [00:01:13.699,768] <err> os: s[ 4]:  0x20017a78  s[ 5]:  0x00000000  s[ 6]:  0x00000000  s[ 7]:  0x00000000
HL [00:01:13.699,768] <err> os: s[ 8]:  0x00000000  s[ 9]:  0x00009903  s[10]:  0x00006d6f  s[11]:  0x200033d0
HL [00:01:13.699,798] <err> os: s[12]:  0x00000002  s[13]:  0x200033d0  s[14]:  0x00000002  s[15]:  0x20017a70
HL [00:01:13.699,798] <err> os: fpscr:  0x00000004
HL [00:01:13.699,829] <err> os: Faulting instruction address (r15/pc): 0x00009910
HL [00:01:13.699,829] <err> os: >>> ZEPHYR FATAL ERROR 3: Kernel oops on CPU 0
HL [00:01:13.699,859] <err> os: Current thread: 0x20004208 (sysworkq)
HL [00:01:13.699,859] <err> error_handler: Caught system error -- reason 3. Entering infinite loop

[ovrebekk]

Hi Paul

Thanks for the update. 

Like mentioned earlier we haven't tested the Packetcraft controller with a broadcast stream and an ACL connection concurrently, and it is quite common to see instability issues when using it outside the uses cases for which it was designed. 

I will set aside some time to test this in order to try and figure out what is going on, and if there is something that can be done to improve reliability, but unfortunately I won't be able to start this work until next week. 

I will get back to you as soon as I have some test results to share. 

Feel free to update the case if you make any new discoveries in the mean time

Best regards
Torbjørn

[muli]

Hi ovrebekk 

The thing is, the Packetcraft controller when used with the Zephyr broadcast_audio_sink, it doesn't disconnect at all when it's connected to my Broadcast Assistant. 

The disconnecting is definitely an issue in my case, but it's not in fact the main blocker for me as my Broadcast Assistant has an auto re-connect feature which re-connects successfully.

However, it fails to re-discover the BASS then due to BT_HCI_ERR_INSUFFICIENT_SECURITY.

What's frustrating is that the re-discovery only fails when using the Packetcraft controller or Soft Device controller on the Broadcast Assistant, but not when using the Zephyr controller.

I could just use the Zephyr controller in that case, but it doesn't support PAST:)

Thanks,

Paul