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[73.185.129.58]) by smtp.gmail.com with ESMTPSA id k4sm5126559ior.55.2021.06.12.07.37.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 12 Jun 2021 07:37:41 -0700 (PDT) From: Alex Elder To: subashab@codeaurora.org, stranche@codeaurora.org, davem@davemloft.net, kuba@kernel.org Cc: bjorn.andersson@linaro.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next 3/8] net: qualcomm: rmnet: show that an intermediate sum is zero Date: Sat, 12 Jun 2021 09:37:31 -0500 Message-Id: <20210612143736.3498712-4-elder@linaro.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210612143736.3498712-1-elder@linaro.org> References: <20210612143736.3498712-1-elder@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c index 1b170e9189d8a..51909b8fa8a80 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)) { -- 2.27.0