Date:   Sun, 26 Aug 2018 12:36:02 -0700
From:   syzbot <syzbot+fe62a0c9aa6a85c6de16@...kaller.appspotmail.com>
To:     davem@...emloft.net, linux-kernel@...r.kernel.org,
        linux-sctp@...r.kernel.org, lucien.xin@...il.com,
        marcelo.leitner@...il.com, netdev@...r.kernel.org,
        nhorman@...driver.com, syzkaller-bugs@...glegroups.com,
        vyasevich@...il.com
Subject: Re: KASAN: use-after-free Read in sctp_transport_get_next

syzbot has found a reproducer for the following crash on:

HEAD commit:    2923b27e5424 Merge tag 'libnvdimm-for-4.19_dax-memory-fail..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f01a1e400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3b576e333ca31bb2
dashboard link: https://syzkaller.appspot.com/bug?extid=fe62a0c9aa6a85c6de16
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1022f96a400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13be8b32400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fe62a0c9aa6a85c6de16@...kaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in sctp_transport_get_next+0x11c/0x140  
net/sctp/socket.c:5008
Read of size 8 at addr ffff8801b09a23e0 by task syz-executor305/13769

CPU: 0 PID: 13769 Comm: syz-executor305 Not tainted 4.18.0+ #209
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
  print_address_description+0x6c/0x20b mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
  sctp_transport_get_next+0x11c/0x140 net/sctp/socket.c:5008
  sctp_transport_get_idx net/sctp/socket.c:5022 [inline]
  sctp_for_each_transport+0x152/0x370 net/sctp/socket.c:5083
  sctp_diag_dump+0x3a7/0x620 net/sctp/diag.c:527
  __inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049
  inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065
  netlink_dump+0x519/0xd50 net/netlink/af_netlink.c:2233
  __netlink_dump_start+0x4f1/0x6f0 net/netlink/af_netlink.c:2329
  netlink_dump_start include/linux/netlink.h:213 [inline]
  inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170
  __sock_diag_cmd net/core/sock_diag.c:232 [inline]
  sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263
  netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2454
  sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274
  netlink_unicast_kernel net/netlink/af_netlink.c:1317 [inline]
  netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1343
  netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1908
  sock_sendmsg_nosec net/socket.c:621 [inline]
  sock_sendmsg+0xd5/0x120 net/socket.c:631
  sock_write_iter+0x362/0x5c0 net/socket.c:900
  call_write_iter include/linux/fs.h:1807 [inline]
  do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
  do_iter_write+0x185/0x5f0 fs/read_write.c:959
  vfs_writev+0x1f1/0x360 fs/read_write.c:1004
  do_writev+0x11a/0x310 fs/read_write.c:1039
  __do_sys_writev fs/read_write.c:1112 [inline]
  __se_sys_writev fs/read_write.c:1109 [inline]
  __x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446679
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 7b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5b0050bda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 0000000000446679
RDX: 0000000000000001 RSI: 0000000020000000 RDI: 0000000000000005
RBP: 00000000006dbc40 R08: 000000000000001c R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 0100000000000000 R14: 00007f5b0050c9c0 R15: 00000000006dbd4c

Allocated by task 13750:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
  kmem_cache_alloc_trace+0x152/0x730 mm/slab.c:3620
  kmalloc include/linux/slab.h:513 [inline]
  kzalloc include/linux/slab.h:707 [inline]
  sctp_association_new+0x127/0x2290 net/sctp/associola.c:311
  sctp_sendmsg_new_asoc+0x39e/0x1200 net/sctp/socket.c:1742
  sctp_sendmsg+0x18a5/0x1da0 net/sctp/socket.c:2103
  inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
  sock_sendmsg_nosec net/socket.c:621 [inline]
  sock_sendmsg+0xd5/0x120 net/socket.c:631
  __sys_sendto+0x3d7/0x670 net/socket.c:1786
  __do_sys_sendto net/socket.c:1798 [inline]
  __se_sys_sendto net/socket.c:1794 [inline]
  __x64_sys_sendto+0xe1/0x1a0 net/socket.c:1794
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 13747:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
  __cache_free mm/slab.c:3498 [inline]
  kfree+0xd9/0x210 mm/slab.c:3813
  sctp_association_destroy net/sctp/associola.c:437 [inline]
  sctp_association_put+0x264/0x350 net/sctp/associola.c:885
  sctp_transport_destroy net/sctp/transport.c:180 [inline]
  sctp_transport_put+0x193/0x200 net/sctp/transport.c:332
  sctp_backlog_rcv+0x28e/0xd50 net/sctp/input.c:357
  sk_backlog_rcv include/net/sock.h:931 [inline]
  __release_sock+0x12f/0x3a0 net/core/sock.c:2336
  release_sock+0xad/0x2c0 net/core/sock.c:2849
  sctp_close+0x49c/0xa80 net/sctp/socket.c:1569
  inet_release+0x104/0x1f0 net/ipv4/af_inet.c:428
  inet6_release+0x50/0x70 net/ipv6/af_inet6.c:457
  __sock_release+0xd7/0x250 net/socket.c:579
  sock_close+0x19/0x20 net/socket.c:1139
  __fput+0x36e/0x8c0 fs/file_table.c:278
  ____fput+0x15/0x20 fs/file_table.c:309
  task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:193 [inline]
  exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801b09a23c0
  which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of
  4096-byte region [ffff8801b09a23c0, ffff8801b09a33c0)
The buggy address belongs to the page:
page:ffffea0006c26880 count:1 mapcount:0 mapping:ffff8801dac00dc0 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0006c0f188 ffffea0006bf8108 ffff8801dac00dc0
raw: 0000000000000000 ffff8801b09a23c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801b09a2280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff8801b09a2300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801b09a2380: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                        ^
  ffff8801b09a2400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801b09a2480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

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