From: Xin Long <lucien.xin@gmail.com>
Date: Tue, 12 Feb 2019 18:47:30 +0800

Jianlin reported a panic when running sctp gso over gre over vlan device:

 ...

It was caused by SKB_GSO_CB(skb)->csum_start not set in sctp_gso_segment.
sctp_gso_segment() calls skb_segment() with 'feature | NETIF_F_HW_CSUM',
which causes SKB_GSO_CB(skb)->csum_start not to be set in skb_segment().

For TCP/UDP, when feature supports HW_CSUM, CHECKSUM_PARTIAL will be set
and gso_reset_checksum will be called to set SKB_GSO_CB(skb)->csum_start.

So SCTP should do the same as TCP/UDP, to call gso_reset_checksum() when
computing checksum in sctp_gso_segment.

Reported-by: Jianlin Shi <redacted>
Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks.