| Message ID | 1568605619-22219-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 00b368502d18f790ab715e055869fd4bb7484a9b |
| Headers | show |
| Series | [1/1] xen-netfront: do not assume sk_buff_head list is empty in error handling | expand |
From: Dongli Zhang <dongli.zhang@oracle.com> Date: Mon, 16 Sep 2019 11:46:59 +0800 > 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> Applied and queued up for -stable.
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index 8d33970..5f5722b 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -906,7 +906,7 @@ static RING_IDX xennet_fill_frags(struct netfront_queue *queue, __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; }
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> --- drivers/net/xen-netfront.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)