Introduce skb->csum_not_inet to identify not-yet-checksummed SCTP packets.
Use this bit in combination with netdev feature bit in validate_xmit_skb,
to discriminate whether skb needs crc32c or 2-complement Internet Checksum
(or none of the two, when the underlying device can do checksum offload).

Signed-off-by: Davide Caratti <redacted>
---
 include/linux/skbuff.h                |  1 +
 net/core/dev.c                        | 14 ++++++++++++--
 net/netfilter/ipvs/ip_vs_proto_sctp.c |  1 +
 net/netfilter/nf_nat_proto_sctp.c     |  1 +
 net/sched/act_csum.c                  |  1 +
 net/sctp/output.c                     |  1 +
 6 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0671131..236b7d9 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -759,6 +759,7 @@ struct sk_buff {
        __u8                    tc_redirected:1;
        __u8                    tc_from_ingress:1;
 #endif
+       __u8                    csum_not_inet:1;

 #ifdef CONFIG_NET_SCHED
        __u16                   tc_index;       /* traffic control index */

diff --git a/net/core/dev.c b/net/core/dev.c
index b9fb843..fae3217 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -2614,6 +2614,7 @@ int skb_sctp_csum_help(struct sk_buff *skb)
        }
        *(__le32 *)(skb->data + offset) = crc32c_csum;
        skb->ip_summed = CHECKSUM_NONE;
+       skb->csum_not_inet = 0;
 out:
        return ret;
 }

@@ -2960,6 +2961,16 @@ static struct sk_buff *validate_xmit_vlan(struct sk_buff *skb,
        return skb;
 }

+static int skb_csum_hwoffload_help(struct sk_buff *skb,
+                                  netdev_features_t features)
+{
+       if (unlikely(skb->csum_not_inet))
+               return !(features & NETIF_F_SCTP_CRC) ?
+                               skb_sctp_csum_help(skb) : 0;
+

+       return !(features & NETIF_F_CSUM_MASK) ? skb_checksum_help(skb) : 0;
+}
+
 static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device *dev)
 {
        netdev_features_t features;

@@ -2995,8 +3006,7 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
                        else
                                skb_set_transport_header(skb,
                                                         skb_checksum_start_offset(skb));
-                       if (!(features & NETIF_F_CSUM_MASK) &&
-                           skb_checksum_help(skb))
+                       if (skb_csum_hwoffload_help(skb, features))
                                goto out_kfree_skb;
                }
        }

diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
index d952d67..4972a60 100644
--- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c

@@ -81,6 +81,7 @@ static void sctp_nat_csum(struct sk_buff *skb, sctp_sctphdr_t *sctph,
                          unsigned int sctphoff)
 {
        sctph->checksum = sctp_compute_cksum(skb, sctphoff);
+       skb->csum_not_inet = 0;
        skb->ip_summed = CHECKSUM_UNNECESSARY;
 }

diff --git a/net/netfilter/nf_nat_proto_sctp.c b/net/netfilter/nf_nat_proto_sctp.c
index 31d3586..9459b88 100644
--- a/net/netfilter/nf_nat_proto_sctp.c
+++ b/net/netfilter/nf_nat_proto_sctp.c

@@ -49,6 +49,7 @@ sctp_manip_pkt(struct sk_buff *skb,

        if (skb->ip_summed != CHECKSUM_PARTIAL) {
                hdr->checksum = sctp_compute_cksum(skb, hdroff);
+               skb->csum_not_inet = 0;
                skb->ip_summed = CHECKSUM_NONE;
        }

diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
index e978ccd4..85cb150 100644
--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c

@@ -337,6 +337,7 @@ static int tcf_csum_sctp(struct sk_buff *skb, unsigned int ihl,

        sctph->checksum = sctp_compute_cksum(skb,
                                             skb_network_offset(skb) + ihl);
+       skb->csum_not_inet = 0;
        skb->ip_summed = CHECKSUM_NONE;

        return 1;

diff --git a/net/sctp/output.c b/net/sctp/output.c
index 814eac0..0dc227b 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c

@@ -528,6 +528,7 @@ static int sctp_packet_pack(struct sctp_packet *packet,
        } else {
 chksum:
                head->ip_summed = CHECKSUM_PARTIAL;
+               head->csum_not_inet = 1;
                head->csum_start = skb_transport_header(head) - head->head;
                head->csum_offset = offsetof(struct sctphdr, checksum);
        }
--

2.7.4