[Xen-devel] [PATCH] xen/netfront: don't bug in case of too many frags

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/net/xen-netfront.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 9407acbd19a9..f17f602e6171 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -908,7 +908,11 @@ 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),
@@ -1045,6 +1049,8 @@ static int xennet_poll(struct napi_struct *napi, int 
budget)
                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;
-- 
2.16.4


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