Re: kernel panic happens when disconnecting Bluetooth headset

[Marcel Holtmann <marcel@holtmann.org>]

Hi Andrei,

> Processing a RFCOMM UA frame when the socket is closed and we were not
> the
> RFCOMM initiator would cause rfcomm_session_put() to be called twice
> during
> rfcomm_process_rx(). This would cause a kernel panic in
> rfcomm_session_close.
> 
> This could be easily reproduced during disconnect with devices such as
> Motorola H270 that send RFCOMM UA followed quickly by L2CAP disconnect
> request.
> This hcidump for this looks like:
> 
> 2009-09-21 17:22:37.788895 < ACL data: handle 1 flags 0x02 dlen 8
>    L2CAP(d): cid 0x0041 len 4 [psm 3]
>      RFCOMM(s): DISC: cr 0 dlci 20 pf 1 ilen 0 fcs 0x7d
> 2009-09-21 17:22:37.906204 > HCI Event: Number of Completed Packets
> (0x13)
> plen 5
>    handle 1 packets 1
> 2009-09-21 17:22:37.933090 > ACL data: handle 1 flags 0x02 dlen 8
>    L2CAP(d): cid 0x0040 len 4 [psm 3]
>      RFCOMM(s): UA: cr 0 dlci 20 pf 1 ilen 0 fcs 0x57
> 2009-09-21 17:22:38.636764 < ACL data: handle 1 flags 0x02 dlen 8
>    L2CAP(d): cid 0x0041 len 4 [psm 3]
>      RFCOMM(s): DISC: cr 0 dlci 0 pf 1 ilen 0 fcs 0x9c
> 2009-09-21 17:22:38.744125 > HCI Event: Number of Completed Packets
> (0x13)
> plen 5
>    handle 1 packets 1
> 2009-09-21 17:22:38.763687 > ACL data: handle 1 flags 0x02 dlen 8
>    L2CAP(d): cid 0x0040 len 4 [psm 3]
>      RFCOMM(s): UA: cr 0 dlci 0 pf 1 ilen 0 fcs 0xb6
> 2009-09-21 17:22:38.783554 > ACL data: handle 1 flags 0x02 dlen 12
>    L2CAP(s): Disconn req: dcid 0x0040 scid 0x0041
> 
> Avoid calling rfcomm_session_put() twice by skipping this call
> in rfcomm_recv_ua() if the socket is closed.
> 
> Picked from:
> http://android.git.kernel.org/?p=kernel/common.git;a=commit;h=1048e007842da2d6440679e1ca80f45438a6369d
> 
> Signed-off-by: Nick Pelly <npelly@google.com>
> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> ---
>  net/bluetooth/rfcomm/core.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
> index 0313e88..56ffcb8 100644
> --- a/net/bluetooth/rfcomm/core.c
> +++ b/net/bluetooth/rfcomm/core.c
> @@ -1148,7 +1148,8 @@ static int rfcomm_recv_ua(struct rfcomm_session
> *s, u8 dlci)
>                         break;
>  
>                 case BT_DISCONN:
> -                       rfcomm_session_put(s);
> +                       if (s->sock->sk->sk_state != BT_CLOSED)
> +                               rfcomm_session_put(s);
>                         break;
>                 }
>         } 

I am not a big fan of conditionally decreasing reference counts. I do
think it would be better to fix this by holding an extra pair of
reference counts or actually fixing the imbalance. What about the other
patches I proposed?

Regards

Marcel