• Xie He's avatar
    drivers/net/wan/hdlc_x25: Added needed_headroom and a skb->len check · 77b981c8
    Xie He authored
    1. Added a skb->len check
    
    This driver expects upper layers to include a pseudo header of 1 byte
    when passing down a skb for transmission. This driver will read this
    1-byte header. This patch added a skb->len check before reading the
    header to make sure the header exists.
    
    2. Added needed_headroom and set hard_header_len to 0
    
    When this driver transmits data,
      first this driver will remove a pseudo header of 1 byte,
      then the lapb module will prepend the LAPB header of 2 or 3 bytes.
    So the value of needed_headroom in this driver should be 3 - 1.
    
    Because this driver has no header_ops, according to the logic of
    af_packet.c, the value of hard_header_len should be 0.
    
    Reason of setting needed_headroom and hard_header_len at this place:
    
    This driver is written using the API of the hdlc module, the hdlc
    module enables this driver (the protocol driver) to run on any hardware
    that has a driver (the hardware driver) written using the API of the
    hdlc module.
    
    Two other hdlc protocol drivers - hdlc_ppp and hdlc_raw_eth, also set
    things like hard_header_len at this place. In hdlc_ppp, it sets
    hard_header_len after attach_hdlc_protocol and before setting dev->type.
    In hdlc_raw_eth, it sets hard_header_len by calling ether_setup after
    attach_hdlc_protocol and after memcpy the settings.
    
    3. Reset needed_headroom when detaching protocols (in hdlc.c)
    
    When detaching a protocol from a hardware device, the hdlc module will
    reset various parameters of the device (including hard_header_len) to
    the default values. We add needed_headroom here so that needed_headroom
    will also be reset.
    
    Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
    Cc: Martin Schiller <ms@dev.tdt.de>
    Cc: Andrew Hendry <andrew.hendry@gmail.com>
    Signed-off-by: default avatarXie He <xie.he.0141@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    77b981c8
hdlc.c 8.03 KB