Hello,

syzbot hit the following crash on net-next commit
fd372a7a9e5e9d8011a0222d10edd3523abcd3b1 (Thu Mar 8 19:43:48 2018 +0000)
Merge tag 'mlx5-updates-2018-02-28-2' of  
git://git.kernel.org/pub/scm/linux/kernel/git/mellanox/linux

So far this crash happened 2 times on net-next.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+a4e4112c3aff00c8cfd8@syzkaller.appspotmail.com
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IPVS: ftp: loaded support on port[0] = 21
IPVS: ftp: loaded support on port[0] = 21
IPVS: ftp: loaded support on port[0] = 21
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: use-after-free in sctp_association_free+0x7b7/0x930  
net/sctp/associola.c:332
Read of size 8 at addr ffff8801d8006ae0 by task syzkaller914861/4202

CPU: 1 PID: 4202 Comm: syzkaller914861 Not tainted 4.16.0-rc4+ #258
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+0x194/0x24d lib/dump_stack.c:53
  print_address_description+0x73/0x250 mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report+0x23c/0x360 mm/kasan/report.c:412
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
  sctp_association_free+0x7b7/0x930 net/sctp/associola.c:332
  sctp_sendmsg+0xc67/0x1a80 net/sctp/socket.c:2075
  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
  sock_sendmsg_nosec net/socket.c:629 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:639
  SYSC_sendto+0x361/0x5c0 net/socket.c:1748
  SyS_sendto+0x40/0x50 net/socket.c:1716
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x446d09
RSP: 002b:00007f5dbac21da8 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000006e29fc RCX: 0000000000446d09
RDX: 0000000000000001 RSI: 0000000020000340 RDI: 0000000000000003
RBP: 00000000006e29f8 R08: 00000000204d9000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000216 R12: 0000000000000000
R13: 00007fff7b26fb1f R14: 00007f5dbac229c0 R15: 00000000006e2b60

Allocated by task 4202:
  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:552
  kmem_cache_alloc_trace+0x136/0x740 mm/slab.c:3607
  kmalloc include/linux/slab.h:512 [inline]
  kzalloc include/linux/slab.h:701 [inline]
  sctp_association_new+0x114/0x2130 net/sctp/associola.c:308
  sctp_sendmsg_new_asoc+0x2e6/0x1000 net/sctp/socket.c:1705
  sctp_sendmsg+0x1450/0x1a80 net/sctp/socket.c:2046
  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
  sock_sendmsg_nosec net/socket.c:629 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:639
  SYSC_sendto+0x361/0x5c0 net/socket.c:1748
  SyS_sendto+0x40/0x50 net/socket.c:1716
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 4202:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
  set_track mm/kasan/kasan.c:459 [inline]
  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
  __cache_free mm/slab.c:3485 [inline]
  kfree+0xd9/0x260 mm/slab.c:3800
  sctp_association_destroy net/sctp/associola.c:434 [inline]
  sctp_association_put+0x21c/0x2f0 net/sctp/associola.c:883
  sctp_wait_for_sndbuf net/sctp/socket.c:8179 [inline]
  sctp_sendmsg_to_asoc+0x1693/0x1e80 net/sctp/socket.c:1904
  sctp_sendmsg+0xc3e/0x1a80 net/sctp/socket.c:2073
  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
  sock_sendmsg_nosec net/socket.c:629 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:639
  SYSC_sendto+0x361/0x5c0 net/socket.c:1748
  SyS_sendto+0x40/0x50 net/socket.c:1716
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801d8006ac0
  which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of
  4096-byte region [ffff8801d8006ac0, ffff8801d8007ac0)
The buggy address belongs to the page:
page:ffffea0007600180 count:1 mapcount:0 mapping:ffff8801d8006ac0 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d8006ac0 0000000000000000 0000000100000001
raw: ffffea0007600120 ffffea0007606c20 ffff8801dac00dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801d8006980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff8801d8006a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801d8006a80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                        ^
  ffff8801d8006b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801d8006b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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