Re: [PATCH] Bluetooth: Fix for L2CAP/LE/CFC/BV-15-C

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Marcel,

On Fri, Feb 26, 2021 at 12:23 PM Marcel Holtmann <marcel@holtmann.org> wrote:
>
> Hi Magdalena,
>
> > This is required for the qualification test L2CAP/LE/CFC/BV-15-C
> >
> > Implementation does not allow to set different key size for SMP and
> > L2CAP, which is needed for a current specification of the test. This fix
> > workarounds it with the debugfs variable le_l2cap_min_key_size.
> >
> > Logs from the test when the IUT uses a min and max l2cap encryption key size 16.
> > $ echo 16 > /sys/kernel/debug/bluetooth/hci0/le_l2cap_min_key_size
> > The lower tester uses a key size 7.
> >
> >> ACL Data RX: Handle 99 flags 0x02 dlen 11                #34 [hci0] 25.007392
> >      SMP: Pairing Request (0x01) len 6
> >        IO capability: DisplayYesNo (0x01)
> >        OOB data: Authentication data not present (0x00)
> >        Authentication requirement: Bonding, No MITM, SC, No Keypresses (0x09)
> >        Max encryption key size: 7
> >        Initiator key distribution: <none> (0x00)
> >        Responder key distribution: <none> (0x00)
> > < ACL Data TX: Handle 99 flags 0x00 dlen 11                #35 [hci0] 25.007591
> >      SMP: Pairing Response (0x02) len 6
> >        IO capability: KeyboardDisplay (0x04)
> >        OOB data: Authentication data not present (0x00)
> >        Authentication requirement: Bonding, No MITM, SC, No Keypresses (0x09)
> >        Max encryption key size: 16
> >        Initiator key distribution: <none> (0x00)
> >        Responder key distribution: <none> (0x00)
> > @ MGMT Event: New Long Term Key (0x000a) plen 37      {0x0001} [hci0] 28.788872
> >        Store hint: Yes (0x01)
> >        LE Address: C0:DE:C0:FF:FF:01 (OUI C0-DE-C0)
> >        Key type: Unauthenticated key from P-256 (0x02)
> >        Master: 0x00
> >        Encryption size: 7
> >        Diversifier: 0000
> >        Randomizer: 0000000000000000
> >        Key: 529e11e8c7b9f5000000000000000000
> >
> > <snip>
> >
> > After pairing with key size 7, L2CAP connection is requested which
> > requires key size 16.
> >
> >> ACL Data RX: Handle 99 flags 0x02 dlen 18                #56 [hci0] 34.998084
> >      LE L2CAP: LE Connection Request (0x14) ident 3 len 10
> >        PSM: 244 (0x00f4)
> >        Source CID: 64
> >        MTU: 256
> >        MPS: 284
> >        Credits: 1
> > < ACL Data TX: Handle 99 flags 0x00 dlen 18                #57 [hci0] 34.998325
> >      LE L2CAP: LE Connection Response (0x15) ident 3 len 10
> >        Destination CID: 0
> >        MTU: 0
> >        MPS: 0
> >        Credits: 0
> >        Result: Connection refused - insufficient encryption key size (0x0007)
> >
> > Signed-off-by: Magdalena Kasenberg <magdalena.kasenberg@codecoup.pl>
> > Reviewed-by: Szymon Janc <szymon.janc@codecoup.pl>
> > Cc: Szymon Janc <szymon.janc@codecoup.pl>
> > ---
> > include/net/bluetooth/hci_core.h |  1 +
> > net/bluetooth/hci_core.c         |  1 +
> > net/bluetooth/hci_debugfs.c      | 30 ++++++++++++++++++++++++++++++
> > net/bluetooth/l2cap_core.c       | 25 +++++++++++++++++++++++++
> > 4 files changed, 57 insertions(+)
> >
> > diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
> > index ebdd4afe30d2..0bf0543efec5 100644
> > --- a/include/net/bluetooth/hci_core.h
> > +++ b/include/net/bluetooth/hci_core.h
> > @@ -379,6 +379,7 @@ struct hci_dev {
> >       __u16           auth_payload_timeout;
> >       __u8            min_enc_key_size;
> >       __u8            max_enc_key_size;
> > +     __u8            le_l2cap_min_key_size;
> >       __u8            pairing_opts;
> >       __u8            ssp_debug_mode;
> >       __u8            hw_error_code;
> > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> > index b0d9c36acc03..9ef4b39b380c 100644
> > --- a/net/bluetooth/hci_core.c
> > +++ b/net/bluetooth/hci_core.c
> > @@ -3788,6 +3788,7 @@ struct hci_dev *hci_alloc_dev(void)
> >       hdev->conn_info_max_age = DEFAULT_CONN_INFO_MAX_AGE;
> >       hdev->auth_payload_timeout = DEFAULT_AUTH_PAYLOAD_TIMEOUT;
> >       hdev->min_enc_key_size = HCI_MIN_ENC_KEY_SIZE;
> > +     hdev->le_l2cap_min_key_size = HCI_MIN_ENC_KEY_SIZE;
>
> so I am not a fan of doing this with another variable and managing through debugfs. Can we pass the qualification test case by using BT_SECURITY_FIPS (which will enforce 128-bit key size)?

I guess that will depend if PTS supports MITM which afaik it is
required with BT_SECURITY_FIPS, from the logs it looks like it doesn't
support it so we end up with an unauthenticated key so the error would
probably be different.

> If not then we might want to add a socket option to set min/max encryption key size requirement on a per socket basis.

Yep, it seems to be a common trend to have such tests on upper layers
(ATT/GATT also have such encryption key size), even though it is more
of a GAP test and perhaps could have been done at SMP level.

>
> Regards
>
> Marcel
>


-- 
Luiz Augusto von Dentz