xen/netfront: don't bug in case of too many frags

commit ad4f15dc2c70b1de5e0a64d27335962fbc9cf71c upstream.

Commit 57f230ab04d291 ("xen/netfront: raise max number of slots in
xennet_get_responses()") raised the max number of allowed slots by one.
This seems to be problematic in some configurations with netback using
a larger MAX_SKB_FRAGS value (e.g. old Linux kernel with MAX_SKB_FRAGS
defined as 18 instead of nowadays 17).

Instead of BUG_ON() in this case just fall back to retransmission.

Fixes: 57f230ab04d291 ("xen/netfront: raise max number of slots in xennet_get_responses()")
Cc: stable@vger.kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index d80343429de5f22fa06aa168d849ddb90610d953..1a40fc3517a8f0b6d443c5e16c94b18c700a4847 100644 (file)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -907,7 +907,11 @@ static RING_IDX xennet_fill_frags(struct netfront_queue *queue,
                        BUG_ON(pull_to <= skb_headlen(skb));
                        __pskb_pull_tail(skb, pull_to - skb_headlen(skb));
                }
-               BUG_ON(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS);
+               if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) {
+                       queue->rx.rsp_cons = ++cons;
+                       kfree_skb(nskb);
+                       return ~0U;
+               }
 
                skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
                                skb_frag_page(nfrag),
@@ -1044,6 +1048,8 @@ err:
                skb->len += rx->status;
 
                i = xennet_fill_frags(queue, skb, &tmpq);
+               if (unlikely(i == ~0U))
+                       goto err;
 
                if (rx->flags & XEN_NETRXF_csum_blank)
                        skb->ip_summed = CHECKSUM_PARTIAL;