syzbot has bisected this bug to:

commit 89664c623617b1d34447a927ac7871ddf3db29d3
Author: Xin Long [off-list ref]
Date:   Sun Mar 3 09:54:53 2019 +0000

     sctp: sctp_sock_migrate() returns error if sctp_bind_addr_dup() fails

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17b17777200000
start commit:   89664c62 sctp: sctp_sock_migrate() returns error if sctp_b..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=14717777200000
console output: https://syzkaller.appspot.com/x/log.txt?x=10717777200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b613f0327d980b6b
dashboard link: https://syzkaller.appspot.com/bug?extid=85e0b422ff140b03672a
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12613b13200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10f1884d200000

Reported-by: syzbot+85e0b422ff140b03672a@syzkaller.appspotmail.com
Fixes: 89664c62 ("sctp: sctp_sock_migrate() returns error if  
sctp_bind_addr_dup() fails")