Hello,

syzkaller hit the following crash on  
37759fa6d0fa9e4d6036d19ac12f555bfc0aeafd
git://git.cmpxchg.org/linux-mmots.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


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Reported-by: syzbot+71d74a5406d02057d559@syzkaller.appspotmail.com
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==================================================================
BUG: KASAN: use-after-free in __tcp_hdrlen include/linux/tcp.h:35 [inline]
BUG: KASAN: use-after-free in tcp_hdrlen include/linux/tcp.h:40 [inline]
BUG: KASAN: use-after-free in qdisc_pkt_len_init net/core/dev.c:3160  
[inline]
BUG: KASAN: use-after-free in __dev_queue_xmit+0x20d3/0x2200  
net/core/dev.c:3465
Read of size 2 at addr ffff8801cb360d38 by task syzkaller769484/3147

CPU: 0 PID: 3147 Comm: syzkaller769484 Not tainted 4.15.0-rc4-mm1+ #49
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:256
  kasan_report_error mm/kasan/report.c:355 [inline]
  kasan_report+0x23b/0x360 mm/kasan/report.c:413
  __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:432
  __tcp_hdrlen include/linux/tcp.h:35 [inline]
  tcp_hdrlen include/linux/tcp.h:40 [inline]
  qdisc_pkt_len_init net/core/dev.c:3160 [inline]
  __dev_queue_xmit+0x20d3/0x2200 net/core/dev.c:3465
  dev_queue_xmit+0x17/0x20 net/core/dev.c:3554
  packet_snd net/packet/af_packet.c:2943 [inline]
  packet_sendmsg+0x3ad5/0x60a0 net/packet/af_packet.c:2968
  sock_sendmsg_nosec net/socket.c:628 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:638
  sock_write_iter+0x31a/0x5d0 net/socket.c:907
  call_write_iter include/linux/fs.h:1776 [inline]
  new_sync_write fs/read_write.c:469 [inline]
  __vfs_write+0x684/0x970 fs/read_write.c:482
  vfs_write+0x189/0x510 fs/read_write.c:544
  SYSC_write fs/read_write.c:589 [inline]
  SyS_write+0xef/0x220 fs/read_write.c:581
  entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x444b89
RSP: 002b:00000000007eff78 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fff91d02bb0 RCX: 0000000000444b89
RDX: 000000000000005d RSI: 0000000020384000 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000120080522 R09: 0000000120080522
R10: 0000000120080522 R11: 0000000000000293 R12: 0000000000402780
R13: 0000000000402810 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 1643:
  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:3607
  kmalloc include/linux/slab.h:516 [inline]
  kzalloc include/linux/slab.h:705 [inline]
  kernfs_fop_open+0x357/0xeb0 fs/kernfs/file.c:648
  do_dentry_open+0x667/0xd40 fs/open.c:752
  vfs_open+0x107/0x220 fs/open.c:866
  do_last fs/namei.c:3397 [inline]
  path_openat+0x1151/0x3530 fs/namei.c:3537
  do_filp_open+0x25b/0x3b0 fs/namei.c:3572
  do_sys_open+0x502/0x6d0 fs/open.c:1059
  SYSC_open fs/open.c:1077 [inline]
  SyS_open+0x2d/0x40 fs/open.c:1072
  entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 1643:
  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:3485 [inline]
  kfree+0xd6/0x260 mm/slab.c:3800
  kernfs_fop_release+0x13f/0x180 fs/kernfs/file.c:783
  __fput+0x327/0x7e0 fs/file_table.c:209
  ____fput+0x15/0x20 fs/file_table.c:243
  task_work_run+0x199/0x270 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
  exit_to_usermode_loop+0x275/0x2f0 arch/x86/entry/common.c:165
  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
  syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
  entry_SYSCALL_64_fastpath+0x94/0x96

The buggy address belongs to the object at ffff8801cb360cc0
  which belongs to the cache kmalloc-512 of size 512
The buggy address is located 120 bytes inside of
  512-byte region [ffff8801cb360cc0, ffff8801cb360ec0)
The buggy address belongs to the page:
page:ffffea00072cd800 count:1 mapcount:0 mapping:ffff8801cb360040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801cb360040 0000000000000000 0000000100000006
raw: ffffea00072bb6a0 ffffea00072bf720 ffff8801dac00940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801cb360c00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
  ffff8801cb360c80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ffff8801cb360d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                         ^
  ffff8801cb360d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801cb360e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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