From: Dongli Zhang dongli.zhang@oracle.com
[ Upstream commit 00b368502d18f790ab715e055869fd4bb7484a9b ]
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: ad4f15dc2c70 ("xen/netfront: don't bug in case of too many frags") Signed-off-by: Dongli Zhang dongli.zhang@oracle.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/xen-netfront.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -909,7 +909,7 @@ static RING_IDX xennet_fill_frags(struct __pskb_pull_tail(skb, pull_to - skb_headlen(skb)); } if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) { - queue->rx.rsp_cons = ++cons; + queue->rx.rsp_cons = ++cons + skb_queue_len(list); kfree_skb(nskb); return ~0U; }