• Dongli Zhang's avatar
    xen-netfront: do not assume sk_buff_head list is empty in error handling · 00b36850
    Dongli Zhang authored
    When skb_shinfo(skb) is not able to cache extra fragment (that is,
    skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS), xennet_fill_frags() assumes
    the sk_buff_head list is already empty. As a result, cons is increased only
    by 1 and returns to error handling path in xennet_poll().
    
    However, if the sk_buff_head list is not empty, queue->rx.rsp_cons may be
    set incorrectly. That is, queue->rx.rsp_cons would point to the rx ring
    buffer entries whose queue->rx_skbs[i] and queue->grant_rx_ref[i] are
    already cleared to NULL. This leads to NULL pointer access in the next
    iteration to process rx ring buffer entries.
    
    Below is how xennet_poll() does error handling. All remaining entries in
    tmpq are accounted to queue->rx.rsp_cons without assuming how many
    outstanding skbs are remained in the list.
    
     985 static int xennet_poll(struct napi_struct *napi, int budget)
    ... ...
    1032           if (unlikely(xennet_set_skb_gso(skb, gso))) {
    1033                   __skb_queue_head(&tmpq, skb);
    1034                   queue->rx.rsp_cons += skb_queue_len(&tmpq);
    1035                   goto err;
    1036           }
    
    It is better to always have the error handling in the same way.
    
    Fixes: ad4f15dc ("xen/netfront: don't bug in case of too many frags")
    Signed-off-by: default avatarDongli Zhang <dongli.zhang@oracle.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    00b36850
xen-netfront.c 55 KB