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From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
Date: Sat, 13 Jul 2019 12:38:02 +0200
Subject: [PATCH 3/4] net: Transmit zero UDP checksum as 0xFFFF
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RH-Author: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: <20190713123802.23932-3-philmd@redhat.com>
Patchwork-id: 89509
O-Subject: [RHEL-7.7 qemu-kvm PATCH 2/2] net: Transmit zero UDP checksum as 0xFFFF
Bugzilla: 1270166
RH-Acked-by: Xiao Wang <jasowang@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>

From: Ed Swierk <eswierk@skyportsystems.com>

The checksum algorithm used by IPv4, TCP and UDP allows a zero value
to be represented by either 0x0000 and 0xFFFF. But per RFC 768, a zero
UDP checksum must be transmitted as 0xFFFF because 0x0000 is a special
value meaning no checksum.

Substitute 0xFFFF whenever a checksum is computed as zero when
modifying a UDP datagram header. Doing this on IPv4 and TCP checksums
is unnecessary but legal. Add a wrapper for net_checksum_finish() that
makes the substitution.

(We can't just change net_checksum_finish(), as that function is also
used by receivers to verify checksums, and in that case the expected
value is always 0x0000.)

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 0dacea92d26c31d453c58de2e99c178fee554166)
[PMD: conflicts: hw/net/net_rx_pkt.c hw/net/vmxnet3.c]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/net/e1000.c         | 2 +-
 hw/net/vmxnet_tx_pkt.c | 2 +-
 include/net/checksum.h | 6 ++++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/hw/net/e1000.c b/hw/net/e1000.c
index 711d369..d876949 100644
--- a/hw/net/e1000.c
+++ b/hw/net/e1000.c
@@ -442,7 +442,7 @@ putsum(uint8_t *data, uint32_t n, uint32_t sloc, uint32_t css, uint32_t cse)
         n = cse + 1;
     if (sloc < n-1) {
         sum = net_checksum_add(n-css, data+css);
-        stw_be_p(data + sloc, net_checksum_finish(sum));
+        stw_be_p(data + sloc, net_checksum_finish_nozero(sum));
     }
 }
 
diff --git a/hw/net/vmxnet_tx_pkt.c b/hw/net/vmxnet_tx_pkt.c
index fc01e4d..03f34cf 100644
--- a/hw/net/vmxnet_tx_pkt.c
+++ b/hw/net/vmxnet_tx_pkt.c
@@ -437,7 +437,7 @@ static void vmxnet_tx_pkt_do_sw_csum(struct VmxnetTxPkt *pkt)
     csum_cntr += eth_calc_pseudo_hdr_csum(iphdr, csl);
 
     /* Put the checksum obtained into the packet */
-    csum = cpu_to_be16(net_checksum_finish(csum_cntr));
+    csum = cpu_to_be16(net_checksum_finish_nozero(csum_cntr));
     iov_from_buf(iov, iov_len, csum_offset, &csum, sizeof csum);
 }
 
diff --git a/include/net/checksum.h b/include/net/checksum.h
index 80203fb..78b7d9b 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -33,6 +33,12 @@ net_checksum_add(int len, uint8_t *buf)
 }
 
 static inline uint16_t
+net_checksum_finish_nozero(uint32_t sum)
+{
+    return net_checksum_finish(sum) ?: 0xFFFF;
+}
+
+static inline uint16_t
 net_raw_checksum(uint8_t *data, int length)
 {
     return net_checksum_finish(net_checksum_add(length, data));
-- 
1.8.3.1