virtio-net: fix possible unsigned integer overflow

When the single-buffer xdp is loaded and after xdp_linearize_page()
is called, *num_buf becomes 0 and (*num_buf - 1) may overflow into
a large integer in virtnet_build_xdp_buff_mrg(), resulting in
unexpected packet dropping.

Fixes: ef75cb51f139 ("virtio-net: build xdp_buff with multi buffers")
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20230131085004.98687-1-hengqi@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ab5c275965e26ae2278b0655ec7b4e1b6eaf1da1..0f0036b1514d10297c0e33a20a677f330f9a2183 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -723,7 +723,7 @@ static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
  * have enough headroom.
  */
 static struct page *xdp_linearize_page(struct receive_queue *rq,
-                                      u16 *num_buf,
+                                      int *num_buf,
                                       struct page *p,
                                       int offset,
                                       int page_off,
@@ -823,7 +823,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
                if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {
                        int offset = buf - page_address(page) + header_offset;
                        unsigned int tlen = len + vi->hdr_len;
-                       u16 num_buf = 1;
+                       int num_buf = 1;
 
                        xdp_headroom = virtnet_get_headroom(vi);
                        header_offset = VIRTNET_RX_PAD + xdp_headroom;
@@ -996,7 +996,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
                                      void *buf,
                                      unsigned int len,
                                      unsigned int frame_sz,
-                                     u16 *num_buf,
+                                     int *num_buf,
                                      unsigned int *xdp_frags_truesize,
                                      struct virtnet_rq_stats *stats)
 {
@@ -1014,6 +1014,9 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
        xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
                         VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
 
+       if (!*num_buf)
+               return 0;
+
        if (*num_buf > 1) {
                /* If we want to build multi-buffer xdp, we need
                 * to specify that the flags of xdp_buff have the
@@ -1027,10 +1030,10 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
                shinfo->xdp_frags_size = 0;
        }
 
-       if ((*num_buf - 1) > MAX_SKB_FRAGS)
+       if (*num_buf > MAX_SKB_FRAGS + 1)
                return -EINVAL;
 
-       while ((--*num_buf) >= 1) {
+       while (--*num_buf > 0) {
                buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
                if (unlikely(!buf)) {
                        pr_debug("%s: rx error: %d buffers out of %d missing\n",
@@ -1083,7 +1086,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                                         struct virtnet_rq_stats *stats)
 {
        struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
-       u16 num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
+       int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
        struct page *page = virt_to_head_page(buf);
        int offset = buf - page_address(page);
        struct sk_buff *head_skb, *curr_skb;