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, as 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 packets and TCP segments 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.) v2: Add a wrapper net_checksum_finish_hdr() rather than duplicating the logic at every caller. Signed-off-by: Ed Swierk <eswi...@skyportsystems.com> --- hw/net/e1000.c | 2 +- hw/net/net_rx_pkt.c | 2 +- hw/net/net_tx_pkt.c | 6 +++--- hw/net/vmxnet3.c | 3 ++- include/net/checksum.h | 7 +++++++ 5 files changed, 14 insertions(+), 6 deletions(-) diff --git a/hw/net/e1000.c b/hw/net/e1000.c index d642314..4e33667 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_hdr(sum)); } } diff --git a/hw/net/net_rx_pkt.c b/hw/net/net_rx_pkt.c index 1019b50..a2b2c2d 100644 --- a/hw/net/net_rx_pkt.c +++ b/hw/net/net_rx_pkt.c @@ -517,7 +517,7 @@ _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_hdr(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..dc95f12 100644 --- a/hw/net/net_tx_pkt.c +++ b/hw/net/net_tx_pkt.c @@ -126,12 +126,12 @@ void net_tx_pkt_update_ip_checksums(struct NetTxPkt *pkt) /* Calculate IP pseudo header checksum */ cntr = eth_calc_ip4_pseudo_hdr_csum(ip_hdr, pkt->payload_len, &cso); - csum = cpu_to_be16(~net_checksum_finish(cntr)); + csum = cpu_to_be16(~net_checksum_finish_hdr(cntr)); } else if (gso_type == VIRTIO_NET_HDR_GSO_TCPV6) { /* Calculate IP pseudo header checksum */ cntr = eth_calc_ip6_pseudo_hdr_csum(ip_hdr, pkt->payload_len, IP_PROTO_TCP, &cso); - csum = cpu_to_be16(~net_checksum_finish(cntr)); + csum = cpu_to_be16(~net_checksum_finish_hdr(cntr)); } else { return; } @@ -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_hdr(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 90f6943..ee7cdeb 100644 --- a/hw/net/vmxnet3.c +++ b/hw/net/vmxnet3.c @@ -970,7 +970,8 @@ 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_hdr(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..9878c8b 100644 --- a/include/net/checksum.h +++ b/include/net/checksum.h @@ -34,6 +34,13 @@ net_checksum_add(int len, uint8_t *buf) } static inline uint16_t +net_checksum_finish_hdr(uint32_t sum) +{ + uint16_t s = net_checksum_finish(sum); + return s ? s : 0xFFFF; +} + +static inline uint16_t net_raw_checksum(uint8_t *data, int length) { return net_checksum_finish(net_checksum_add(length, data)); -- 1.9.1