Use struct sctp_sack_info instead
==================================================================
BUG: KASAN: use-after-free in sctp_association_free+0x7b7/0x930 net/sctp/associola.c:332
Read of size 8 at addr ffff8801d3e6a720 by task syz-executor1/7100

CPU: 1 PID: 7100 Comm: syz-executor1 Not tainted 4.14.0-next-20171114+ #42
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 sctp_association_free+0x7b7/0x930 net/sctp/associola.c:332
 sctp_sendmsg+0x1845/0x32c0 net/sctp/socket.c:2049
 inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
 sock_sendmsg_nosec net/socket.c:632 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:642
 SYSC_sendto+0x358/0x5a0 net/socket.c:1749
 SyS_sendto+0x40/0x50 net/socket.c:1717
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452879
RSP: 002b:00007f586a45dbe8 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000758190 RCX: 0000000000452879
RDX: 0000000000000002 RSI: 0000000020925000 RDI: 0000000000000016
RBP: 0000000000000086 R08: 00000000209e1000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006ee1a8
R13: 00000000ffffffff R14: 00007f586a45e6d4 R15: 0000000000000014

Allocated by task 7100:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3614
 kmalloc include/linux/slab.h:514 [inline]
 kzalloc include/linux/slab.h:703 [inline]
 sctp_association_new+0x114/0x2200 net/sctp/associola.c:308
 sctp_sendmsg+0x1c89/0x32c0 net/sctp/socket.c:1869
 inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
 sock_sendmsg_nosec net/socket.c:632 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:642
 SYSC_sendto+0x358/0x5a0 net/socket.c:1749
 SyS_sendto+0x40/0x50 net/socket.c:1717
 entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 7100:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3492 [inline]
 kfree+0xca/0x250 mm/slab.c:3807
 sctp_association_destroy net/sctp/associola.c:434 [inline]
 sctp_association_put+0x21c/0x2f0 net/sctp/associola.c:883
 sctp_wait_for_sndbuf+0x5e3/0x7c0 net/sctp/socket.c:8033
 sctp_sendmsg+0x2906/0x32c0 net/sctp/socket.c:1973
 inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
 sock_sendmsg_nosec net/socket.c:632 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:642
 SYSC_sendto+0x358/0x5a0 net/socket.c:1749
 SyS_sendto+0x40/0x50 net/socket.c:1717
 entry_SYSCALL_64_fastpath+0x1f/0x96

The buggy address belongs to the object at ffff8801d3e6a700
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of
 4096-byte region [ffff8801d3e6a700, ffff8801d3e6b700)
The buggy address belongs to the page:
page:ffffea00074f9a80 count:1 mapcount:0 mapping:ffff8801d3e6a700 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d3e6a700 0000000000000000 0000000100000001
raw: ffffea00073a9ca0 ffffea000751c220 ffff8801db000dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d3e6a600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d3e6a680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d3e6a700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff8801d3e6a780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d3e6a800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================