From: Alex Elder Date: Sat, 12 Jun 2021 14:37:31 +0000 (-0500) Subject: net: qualcomm: rmnet: show that an intermediate sum is zero X-Git-Tag: accepted/tizen/unified/20230118.172025~6942^2~190^2~5 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=9d0407bc4c9ca7a2378230dd86f8ce90a2b6ad09;p=platform%2Fkernel%2Flinux-rpi.git net: qualcomm: rmnet: show that an intermediate sum is zero This patch simply demonstrates that a checksum value computed when verifying an offloaded transport checksum value for both IPv4 and IPv6 is (normally) 0. It can be squashed into the next patch. Signed-off-by: Alex Elder Signed-off-by: David S. Miller --- diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c index 1b170e9..51909b8 100644 --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c @@ -84,6 +84,11 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb, ip4h->protocol, 0); pseudo_csum = csum16_add(ip_payload_csum, (__force __be16)pseudo_csum); + /* The trailer checksum *includes* the checksum in the transport + * header. Adding that to the pseudo checksum will yield 0xffff + * ("negative 0") if the message arrived intact. + */ + WARN_ON((__sum16)~pseudo_csum); csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field); if (unlikely(!csum_value_final)) { @@ -150,6 +155,10 @@ rmnet_map_ipv6_dl_csum_trailer(struct sk_buff *skb, length, ip6h->nexthdr, 0); pseudo_csum = csum16_add(ip6_payload_csum, (__force __be16)pseudo_csum); + /* Adding the payload checksum to the pseudo checksum yields 0xffff + * ("negative 0") if the message arrived intact. + */ + WARN_ON((__sum16)~pseudo_csum); csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field); if (unlikely(csum_value_final == 0)) {