[PULL 6/6] virtio-net: Copy received header to buffer

[Jason Wang <jasowang@redhat.com>]

From: Akihiko Odaki <akihiko.odaki@daynix.com>

receive_header() used to cast the const qualifier of the pointer to the
received packet away to modify the header. Avoid this by copying the
received header to buffer.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/net/virtio-net.c | 85 ++++++++++++++++++++++++---------------------
 1 file changed, 46 insertions(+), 39 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 44ea72b50e..bc0f31b666 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1695,41 +1695,44 @@ static void virtio_net_hdr_swap(VirtIODevice *vdev, struct virtio_net_hdr *hdr)
  * cache.
  */
 static void work_around_broken_dhclient(struct virtio_net_hdr *hdr,
-                                        uint8_t *buf, size_t size)
+                                        size_t *hdr_len, const uint8_t *buf,
+                                        size_t buf_size, size_t *buf_offset)
 {
     size_t csum_size = ETH_HLEN + sizeof(struct ip_header) +
                        sizeof(struct udp_header);
 
+    buf += *buf_offset;
+    buf_size -= *buf_offset;
+
     if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /* missing csum */
-        (size >= csum_size && size < 1500) && /* normal sized MTU */
+        (buf_size >= csum_size && buf_size < 1500) && /* normal sized MTU */
         (buf[12] == 0x08 && buf[13] == 0x00) && /* ethertype == IPv4 */
         (buf[23] == 17) && /* ip.protocol == UDP */
         (buf[34] == 0 && buf[35] == 67)) { /* udp.srcport == bootps */
-        net_checksum_calculate(buf, size, CSUM_UDP);
+        memcpy((uint8_t *)hdr + *hdr_len, buf, csum_size);
+        net_checksum_calculate((uint8_t *)hdr + *hdr_len, csum_size, CSUM_UDP);
         hdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
+        *hdr_len += csum_size;
+        *buf_offset += csum_size;
     }
 }
 
-static void receive_header(VirtIONet *n, const struct iovec *iov, int iov_cnt,
-                           const void *buf, size_t size)
+static size_t receive_header(VirtIONet *n, struct virtio_net_hdr *hdr,
+                             const void *buf, size_t buf_size,
+                             size_t *buf_offset)
 {
-    if (n->has_vnet_hdr) {
-        /* FIXME this cast is evil */
-        void *wbuf = (void *)buf;
-        work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
-                                    size - n->host_hdr_len);
+    size_t hdr_len = n->guest_hdr_len;
 
-        if (n->needs_vnet_hdr_swap) {
-            virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
-        }
-        iov_from_buf(iov, iov_cnt, 0, buf, sizeof(struct virtio_net_hdr));
-    } else {
-        struct virtio_net_hdr hdr = {
-            .flags = 0,
-            .gso_type = VIRTIO_NET_HDR_GSO_NONE
-        };
-        iov_from_buf(iov, iov_cnt, 0, &hdr, sizeof hdr);
+    memcpy(hdr, buf, sizeof(struct virtio_net_hdr));
+
+    *buf_offset = n->host_hdr_len;
+    work_around_broken_dhclient(hdr, &hdr_len, buf, buf_size, buf_offset);
+
+    if (n->needs_vnet_hdr_swap) {
+        virtio_net_hdr_swap(VIRTIO_DEVICE(n), hdr);
     }
+
+    return hdr_len;
 }
 
 static int receive_filter(VirtIONet *n, const uint8_t *buf, int size)
@@ -1897,6 +1900,13 @@ static int virtio_net_process_rss(NetClientState *nc, const uint8_t *buf,
     return (index == new_index) ? -1 : new_index;
 }
 
+typedef struct Header {
+    struct virtio_net_hdr_v1_hash virtio_net;
+    struct eth_header eth;
+    struct ip_header ip;
+    struct udp_header udp;
+} Header;
+
 static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
                                       size_t size)
 {
@@ -1906,15 +1916,15 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
     VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE];
     size_t lens[VIRTQUEUE_MAX_SIZE];
     struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE];
-    struct virtio_net_hdr_v1_hash extra_hdr;
+    Header hdr;
     unsigned mhdr_cnt = 0;
     size_t offset, i, guest_offset, j;
     ssize_t err;
 
-    memset(&extra_hdr, 0, sizeof(extra_hdr));
+    memset(&hdr.virtio_net, 0, sizeof(hdr.virtio_net));
 
     if (n->rss_data.enabled && n->rss_data.enabled_software_rss) {
-        int index = virtio_net_process_rss(nc, buf, size, &extra_hdr);
+        int index = virtio_net_process_rss(nc, buf, size, &hdr.virtio_net);
         if (index >= 0) {
             nc = qemu_get_subqueue(n->nic, index % n->curr_queue_pairs);
         }
@@ -1979,21 +1989,18 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
             if (n->mergeable_rx_bufs) {
                 mhdr_cnt = iov_copy(mhdr_sg, ARRAY_SIZE(mhdr_sg),
                                     sg, elem->in_num,
-                                    offsetof(typeof(extra_hdr), hdr.num_buffers),
-                                    sizeof(extra_hdr.hdr.num_buffers));
+                                    offsetof(typeof(hdr),
+                                             virtio_net.hdr.num_buffers),
+                                    sizeof(hdr.virtio_net.hdr.num_buffers));
             }
 
-            receive_header(n, sg, elem->in_num, buf, size);
-            if (n->rss_data.populate_hash) {
-                offset = offsetof(typeof(extra_hdr), hash_value);
-                iov_from_buf(sg, elem->in_num, offset,
-                             (char *)&extra_hdr + offset,
-                             sizeof(extra_hdr.hash_value) +
-                             sizeof(extra_hdr.hash_report));
-            }
-            offset = n->host_hdr_len;
-            total += n->guest_hdr_len;
-            guest_offset = n->guest_hdr_len;
+            guest_offset = n->has_vnet_hdr ?
+                           receive_header(n, (struct virtio_net_hdr *)&hdr,
+                                          buf, size, &offset) :
+                           n->guest_hdr_len;
+
+            iov_from_buf(sg, elem->in_num, 0, &hdr, guest_offset);
+            total += guest_offset;
         } else {
             guest_offset = 0;
         }
@@ -2019,11 +2026,11 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
     }
 
     if (mhdr_cnt) {
-        virtio_stw_p(vdev, &extra_hdr.hdr.num_buffers, i);
+        virtio_stw_p(vdev, &hdr.virtio_net.hdr.num_buffers, i);
         iov_from_buf(mhdr_sg, mhdr_cnt,
                      0,
-                     &extra_hdr.hdr.num_buffers,
-                     sizeof extra_hdr.hdr.num_buffers);
+                     &hdr.virtio_net.hdr.num_buffers,
+                     sizeof hdr.virtio_net.hdr.num_buffers);
     }
 
     for (j = 0; j < i; j++) {
-- 
2.42.0