Bluetooth: split sk_filter in l2cap_sock_recv_cb
During an audit for sk_filter(), we found that rx_busy_skb handling in l2cap_sock_recv_cb() and l2cap_sock_recvmsg() looks not quite as intended. The assumption from commit e328140f ("Bluetooth: Use event-driven approach for handling ERTM receive buffer") is that errors returned from sock_queue_rcv_skb() are due to receive buffer shortage. However, nothing should prevent doing a setsockopt() with SO_ATTACH_FILTER on the socket, that could drop some of the incoming skbs when handled in sock_queue_rcv_skb(). In that case sock_queue_rcv_skb() will return with -EPERM, propagated from sk_filter() and if in L2CAP_MODE_ERTM mode, wrong assumption was that we failed due to receive buffer being full. From that point onwards, due to the to-be-dropped skb being held in rx_busy_skb, we cannot make any forward progress as rx_busy_skb is never cleared from l2cap_sock_recvmsg(), due to the filter drop verdict over and over coming from sk_filter(). Meanwhile, in l2cap_sock_recv_cb() all new incoming skbs are being dropped due to rx_busy_skb being occupied. Instead, just use __sock_queue_rcv_skb() where an error really tells that there's a receive buffer issue. Split the sk_filter() and enable it for non-segmented modes at queuing time since at this point in time the skb has already been through the ERTM state machine and it has been acked, so dropping is not allowed. Instead, for ERTM and streaming mode, call sk_filter() in l2cap_data_rcv() so the packet can be dropped before the state machine sees it. Fixes: e328140f ("Bluetooth: Use event-driven approach for handling ERTM receive buffer") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com> Acked-by: Willem de Bruijn <willemb@google.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
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