• Xie He's avatar
    drivers/net/wan: lapb: Corrected the usage of skb_cow · 8754e137
    Xie He authored
    This patch fixed 2 issues with the usage of skb_cow in LAPB drivers
    "lapbether" and "hdlc_x25":
    
    1) After skb_cow fails, kfree_skb should be called to drop a reference
    to the skb. But in both drivers, kfree_skb is not called.
    
    2) skb_cow should be called before skb_push so that is can ensure the
    safety of skb_push. But in "lapbether", it is incorrectly called after
    skb_push.
    
    More details about these 2 issues:
    
    1) The behavior of calling kfree_skb on failure is also the behavior of
    netif_rx, which is called by this function with "return netif_rx(skb);".
    So this function should follow this behavior, too.
    
    2) In "lapbether", skb_cow is called after skb_push. This results in 2
    logical issues:
       a) skb_push is not protected by skb_cow;
       b) An extra headroom of 1 byte is ensured after skb_push. This extra
          headroom has no use in this function. It also has no use in the
          upper-layer function that this function passes the skb to
          (x25_lapb_receive_frame in net/x25/x25_dev.c).
    So logically skb_cow should instead be called before skb_push.
    
    Cc: Eric Dumazet <edumazet@google.com>
    Cc: Martin Schiller <ms@dev.tdt.de>
    Signed-off-by: default avatarXie He <xie.he.0141@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    8754e137
lapbether.c 10.1 KB