virtio_net: fix error handling for mergeable buffers

Eric Dumazet noticed that if we encounter an error
when processing a mergeable buffer, we don't
dequeue all of the buffers from this packet,
the result is almost sure to be loss of networking.

Jason Wang noticed that we also leak a page and that we don't decrement
the rq buf count, so we won't repost buffers (a resource leak).

Fix both issues.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael Dalton <mwdalton@google.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index acda66169973413090427ff566cb3bcff0e50288..71a2eac7b0396dcdcab5882afb8868dbc35aa478 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -299,35 +299,47 @@ static struct sk_buff *page_to_skb(struct receive_queue *rq,
        return skb;
 }
 
-static int receive_mergeable(struct receive_queue *rq, struct sk_buff *head_skb)
+static struct sk_buff *receive_mergeable(struct net_device *dev,
+                                        struct receive_queue *rq,
+                                        void *buf,
+                                        unsigned int len)
 {
-       struct skb_vnet_hdr *hdr = skb_vnet_hdr(head_skb);
+       struct skb_vnet_hdr *hdr = buf;
+       int num_buf = hdr->mhdr.num_buffers;
+       struct page *page = virt_to_head_page(buf);
+       int offset = buf - page_address(page);
+       struct sk_buff *head_skb = page_to_skb(rq, page, offset, len,
+                                              MERGE_BUFFER_LEN);
        struct sk_buff *curr_skb = head_skb;
-       char *buf;
-       struct page *page;
-       int num_buf, len, offset;
 
-       num_buf = hdr->mhdr.num_buffers;
+       if (unlikely(!curr_skb))
+               goto err_skb;
+
        while (--num_buf) {
-               int num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
+               int num_skb_frags;
+
                buf = virtqueue_get_buf(rq->vq, &len);
                if (unlikely(!buf)) {
-                       pr_debug("%s: rx error: %d buffers missing\n",
-                                head_skb->dev->name, hdr->mhdr.num_buffers);
-                       head_skb->dev->stats.rx_length_errors++;
-                       return -EINVAL;
+                       pr_debug("%s: rx error: %d buffers out of %d missing\n",
+                                dev->name, num_buf, hdr->mhdr.num_buffers);
+                       dev->stats.rx_length_errors++;
+                       goto err_buf;
                }
                if (unlikely(len > MERGE_BUFFER_LEN)) {
                        pr_debug("%s: rx error: merge buffer too long\n",
-                                head_skb->dev->name);
+                                dev->name);
                        len = MERGE_BUFFER_LEN;
                }
+
+               page = virt_to_head_page(buf);
+               --rq->num;
+
+               num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
                if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
                        struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
-                       if (unlikely(!nskb)) {
-                               head_skb->dev->stats.rx_dropped++;
-                               return -ENOMEM;
-                       }
+
+                       if (unlikely(!nskb))
+                               goto err_skb;
                        if (curr_skb == head_skb)
                                skb_shinfo(curr_skb)->frag_list = nskb;
                        else
@@ -341,8 +353,7 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *head_skb)
                        head_skb->len += len;
                        head_skb->truesize += MERGE_BUFFER_LEN;
                }
-               page = virt_to_head_page(buf);
-               offset = buf - (char *)page_address(page);
+               offset = buf - page_address(page);
                if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
                        put_page(page);
                        skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
@@ -351,9 +362,28 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *head_skb)
                        skb_add_rx_frag(curr_skb, num_skb_frags, page,
                                        offset, len, MERGE_BUFFER_LEN);
                }
+       }
+
+       return head_skb;
+
+err_skb:
+       put_page(page);
+       while (--num_buf) {
+               buf = virtqueue_get_buf(rq->vq, &len);
+               if (unlikely(!buf)) {
+                       pr_debug("%s: rx error: %d buffers missing\n",
+                                dev->name, num_buf);
+                       dev->stats.rx_length_errors++;
+                       break;
+               }
+               page = virt_to_head_page(buf);
+               put_page(page);
                --rq->num;
        }
-       return 0;
+err_buf:
+       dev->stats.rx_dropped++;
+       dev_kfree_skb(head_skb);
+       return NULL;
 }
 
 static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
@@ -382,19 +412,9 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
                len -= sizeof(struct virtio_net_hdr);
                skb_trim(skb, len);
        } else if (vi->mergeable_rx_bufs) {
-               struct page *page = virt_to_head_page(buf);
-               skb = page_to_skb(rq, page,
-                                 (char *)buf - (char *)page_address(page),
-                                 len, MERGE_BUFFER_LEN);
-               if (unlikely(!skb)) {
-                       dev->stats.rx_dropped++;
-                       put_page(page);
+               skb = receive_mergeable(dev, rq, buf, len);
+               if (unlikely(!skb))
                        return;
-               }
-               if (receive_mergeable(rq, skb)) {
-                       dev_kfree_skb(skb);
-                       return;
-               }
        } else {
                page = buf;
                skb = page_to_skb(rq, page, 0, len, PAGE_SIZE);