net: sctp: fix checksum marking for outgoing packets

Packets to devices without NETIF_F_SCTP_CSUM (including NETIF_F_NO_CSUM)
should be properly checksummed because the packets can be diverted or
rerouted after construction. This still leaves packets diverted from
NETIF_F_SCTP_CSUM-enabled devices with broken checksums. Fixing this
needs implementing software offload fallback in networking core.

For users of sctp_checksum_disable, skb->ip_summed should be left as
CHECKSUM_NONE and not CHECKSUM_UNNECESSARY as per include/linux/skbuff.h.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/output.c b/net/sctp/output.c
index b4f3cf06d8da7afd6f497d8e3dc1f3e3c7031afd..08b3cead6503c62f91dc8e97d9b817de7a79ffb9 100644 (file)
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -500,23 +500,20 @@ int sctp_packet_transmit(struct sctp_packet *packet)
         * Note: Adler-32 is no longer applicable, as has been replaced
         * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
         */
-       if (!sctp_checksum_disable &&
-           !(dst->dev->features & (NETIF_F_NO_CSUM | NETIF_F_SCTP_CSUM))) {
-               __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
+       if (!sctp_checksum_disable) {
+               if (!(dst->dev->features & NETIF_F_SCTP_CSUM)) {
+                       __u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
 
-               /* 3) Put the resultant value into the checksum field in the
-                *    common header, and leave the rest of the bits unchanged.
-                */
-               sh->checksum = sctp_end_cksum(crc32);
-       } else {
-               if (dst->dev->features & NETIF_F_SCTP_CSUM) {
+                       /* 3) Put the resultant value into the checksum field in the
+                        *    common header, and leave the rest of the bits unchanged.
+                        */
+                       sh->checksum = sctp_end_cksum(crc32);
+               } else {
                        /* no need to seed pseudo checksum for SCTP */
                        nskb->ip_summed = CHECKSUM_PARTIAL;
                        nskb->csum_start = (skb_transport_header(nskb) -
                                            nskb->head);
                        nskb->csum_offset = offsetof(struct sctphdr, checksum);
-               } else {
-                       nskb->ip_summed = CHECKSUM_UNNECESSARY;
                }
        }