[Qemu-devel] [PULL for-2.4 3/7] net/vmxnet3: Fix RX TCP/UDP checksum on partially summed packets

[Stefan Hajnoczi <stefanha@redhat.com>]

From: Dana Rubin <dana.rubin@ravellosystems.com>

Convert partially summed packets to be fully checksummed.

In case csum offloaded packet, vmxnet3 implementation always passes an
RxCompDesc with the "Checksum calculated and found correct" notification
to the OS. This emulates the observed ESXi behavior.

Therefore, if packet has the NEEDS_CSUM bit set, we must calculate and
place a fully computed checksum into the tcp/udp header. Otherwise, the
OS driver will receive a checksum-correct indication but with the actual
tcp/udp checksum field having just the pseudo header csum value.

If host OS performs forwarding, it will forward an incorrectly
checksummed packet.

Signed-off-by: Dana Rubin <dana.rubin@ravellosystems.com>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
Message-id: 1436864116-19154-3-git-send-email-shmulik.ladkani@ravellosystems.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/net/vmxnet3.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/hw/net/vmxnet3.c b/hw/net/vmxnet3.c
index dd22a0a..59b06b8 100644
--- a/hw/net/vmxnet3.c
+++ b/hw/net/vmxnet3.c
@@ -885,6 +885,63 @@ vmxnet3_get_next_rx_descr(VMXNET3State *s, bool is_head,
     }
 }
 
+/* In case packet was csum offloaded (either NEEDS_CSUM or DATA_VALID),
+ * the implementation always passes an RxCompDesc with a "Checksum
+ * calculated and found correct" to the OS (cnc=0 and tuc=1, see
+ * vmxnet3_rx_update_descr). This emulates the observed ESXi behavior.
+ *
+ * Therefore, if packet has the NEEDS_CSUM set, we must calculate
+ * and place a fully computed checksum into the tcp/udp header.
+ * Otherwise, the OS driver will receive a checksum-correct indication
+ * (CHECKSUM_UNNECESSARY), but with the actual tcp/udp checksum field
+ * having just the pseudo header csum value.
+ *
+ * While this is not a problem if packet is destined for local delivery,
+ * in the case the host OS performs forwarding, it will forward an
+ * incorrectly checksummed packet.
+ */
+static void vmxnet3_rx_need_csum_calculate(struct VmxnetRxPkt *pkt,
+                                           const void *pkt_data,
+                                           size_t pkt_len)
+{
+    struct virtio_net_hdr *vhdr;
+    bool isip4, isip6, istcp, isudp;
+    uint8_t *data;
+    int len;
+
+    if (!vmxnet_rx_pkt_has_virt_hdr(pkt)) {
+        return;
+    }
+
+    vhdr = vmxnet_rx_pkt_get_vhdr(pkt);
+    if (!VMXNET_FLAG_IS_SET(vhdr->flags, VIRTIO_NET_HDR_F_NEEDS_CSUM)) {
+        return;
+    }
+
+    vmxnet_rx_pkt_get_protocols(pkt, &isip4, &isip6, &isudp, &istcp);
+    if (!(isip4 || isip6) || !(istcp || isudp)) {
+        return;
+    }
+
+    vmxnet3_dump_virt_hdr(vhdr);
+
+    /* Validate packet len: csum_start + scum_offset + length of csum field */
+    if (pkt_len < (vhdr->csum_start + vhdr->csum_offset + 2)) {
+        VMW_PKPRN("packet len:%d < csum_start(%d) + csum_offset(%d) + 2, "
+                  "cannot calculate checksum",
+                  len, vhdr->csum_start, vhdr->csum_offset);
+        return;
+    }
+
+    data = (uint8_t *)pkt_data + vhdr->csum_start;
+    len = pkt_len - vhdr->csum_start;
+    /* Put the checksum obtained into the packet */
+    stw_be_p(data + vhdr->csum_offset, net_raw_checksum(data, len));
+
+    vhdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
+    vhdr->flags |= VIRTIO_NET_HDR_F_DATA_VALID;
+}
+
 static void vmxnet3_rx_update_descr(struct VmxnetRxPkt *pkt,
     struct Vmxnet3_RxCompDesc *rxcd)
 {
@@ -1898,6 +1955,7 @@ vmxnet3_receive(NetClientState *nc, const uint8_t *buf, size_t size)
 
     if (vmxnet3_rx_filter_may_indicate(s, buf, size)) {
         vmxnet_rx_pkt_set_protocols(s->rx_pkt, buf, size);
+        vmxnet3_rx_need_csum_calculate(s->rx_pkt, buf, size);
         vmxnet_rx_pkt_attach_data(s->rx_pkt, buf, size, s->rx_vlan_stripping);
         bytes_indicated = vmxnet3_indicate_packet(s) ? size : -1;
         if (bytes_indicated < size) {
-- 
2.4.3