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 <address@hidden>
---
v3:
(Reposted to fix patch format)
Leave net_tx_pkt_update_ip_checksums() alone since it's only computing
a partial sum of the IP pseudo-header.
Rename wrapper to net_checksum_finish_nozero() for clarity.
v2:
Add a wrapper net_checksum_finish_hdr() rather than duplicating the
logic at every caller.
---
hw/net/e1000.c | 2 +-
hw/net/net_rx_pkt.c | 2 +-
hw/net/net_tx_pkt.c | 2 +-
hw/net/vmxnet3.c | 3 ++-
include/net/checksum.h | 6 ++++++
5 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/hw/net/e1000.c b/hw/net/e1000.c
index 72a92be..804ec08 100644
--- a/hw/net/e1000.c
+++ b/hw/net/e1000.c
@@ -506,7 +506,7 @@ 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/net_rx_pkt.c b/hw/net/net_rx_pkt.c
index cef1c2e..98a5030 100644
--- a/hw/net/net_rx_pkt.c
+++ b/hw/net/net_rx_pkt.c
@@ -518,7 +518,7 @@ _net_rx_pkt_calc_l4_csum(struct NetRxPkt *pkt)
cntr += net_checksum_add_iov(pkt->vec, pkt->vec_len,
pkt->l4hdr_off, csl, cso);
- csum = net_checksum_finish(cntr);
+ csum = net_checksum_finish_nozero(cntr);
trace_net_rx_pkt_l4_csum_calc_csum(pkt->l4hdr_off, csl, cntr, csum);
diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
index 20b2549..e29c881 100644
--- a/hw/net/net_tx_pkt.c
+++ b/hw/net/net_tx_pkt.c
@@ -486,7 +486,7 @@ static void net_tx_pkt_do_sw_csum(struct NetTxPkt *pkt)
net_checksum_add_iov(iov, iov_len, pkt->virt_hdr.csum_start, csl,
cso);
/* 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/hw/net/vmxnet3.c b/hw/net/vmxnet3.c
index 8c4bae5..cdc307d 100644
--- a/hw/net/vmxnet3.c
+++ b/hw/net/vmxnet3.c
@@ -972,7 +972,8 @@ static void vmxnet3_rx_need_csum_calculate(struct NetRxPkt
*pkt,
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));
+ stw_be_p(data + vhdr->csum_offset,
+ net_checksum_finish_nozero(net_checksum_add(len, data)));
vhdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
vhdr->flags |= VIRTIO_NET_HDR_F_DATA_VALID;
diff --git a/include/net/checksum.h b/include/net/checksum.h
index 7df472c..05a0d27 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -34,6 +34,12 @@ 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));