R13: 00000000004c1cbc R14: 00000000004d3fa8 R15: 0000000000000004
==================================================================
BUG: KASAN: double-free or invalid-free in x25_asy_free+0x37/0x140 drivers/net/wan/x25_asy.c:111
mkiss: ax0: crc mode is auto.

CPU: 1 PID: 22970 Comm: syz-executor4 Not tainted 4.20.0-rc7-next-20181224 #189
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+0x1d3/0x2c6 lib/dump_stack.c:113
 print_address_description.cold.5+0x9/0x1ff mm/kasan/report.c:187
 kasan_report_invalid_free+0x64/0xa0 mm/kasan/report.c:278
 __kasan_slab_free+0x13a/0x150 mm/kasan/common.c:423
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
 __cache_free mm/slab.c:3485 [inline]
 kfree+0xcf/0x230 mm/slab.c:3804
 x25_asy_free+0x37/0x140 drivers/net/wan/x25_asy.c:111
 x25_asy_open_tty+0x6ad/0x7e7 drivers/net/wan/x25_asy.c:572
 tty_ldisc_open.isra.0+0x8b/0xe0 drivers/tty/tty_ldisc.c:460
 tty_set_ldisc+0x2d3/0x6a0 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2323 [inline]
 tty_ioctl+0x39d/0x17d0 drivers/tty/tty_io.c:2583
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4579b9
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc544e88c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc544e88c90 RCX: 00000000004579b9
RDX: 0000000020000040 RSI: 0000000000005423 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc544e896d4
R13: 00000000004c1cbc R14: 00000000004d3fa8 R15: 0000000000000004

Allocated by task 22970:
 save_stack+0x43/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 kasan_kmalloc+0xcb/0xd0 mm/kasan/common.c:482
 __do_kmalloc mm/slab.c:3709 [inline]
 __kmalloc+0x15d/0x760 mm/slab.c:3718
 kmalloc include/linux/slab.h:550 [inline]
 x25_asy_open drivers/net/wan/x25_asy.c:465 [inline]
 x25_asy_open_tty+0x32a/0x7e7 drivers/net/wan/x25_asy.c:570
 tty_ldisc_open.isra.0+0x8b/0xe0 drivers/tty/tty_ldisc.c:460
 tty_set_ldisc+0x2d3/0x6a0 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2323 [inline]
 tty_ioctl+0x39d/0x17d0 drivers/tty/tty_io.c:2583
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 22970:
 save_stack+0x43/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
 __cache_free mm/slab.c:3485 [inline]
 kfree+0xcf/0x230 mm/slab.c:3804
kobject: 'tx-0' (00000000f443890e): kobject_uevent_env
 x25_asy_open drivers/net/wan/x25_asy.c:489 [inline]
 x25_asy_open_tty+0x6a0/0x7e7 drivers/net/wan/x25_asy.c:570
 tty_ldisc_open.isra.0+0x8b/0xe0 drivers/tty/tty_ldisc.c:460
 tty_set_ldisc+0x2d3/0x6a0 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2323 [inline]
 tty_ioctl+0x39d/0x17d0 drivers/tty/tty_io.c:2583
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
kobject: 'tx-0' (00000000f443890e): fill_kobj_path: path = '/devices/virtual/net/ax1/queues/tx-0'
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888098e8cdc0
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 0 bytes inside of
 1024-byte region [ffff888098e8cdc0, ffff888098e8d1c0)
The buggy address belongs to the page:
page:ffffea000263a300 count:1 mapcount:0 mapping:ffff88812c3f0ac0 index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002931208 ffffea00023d3e88 ffff88812c3f0ac0
raw: 0000000000000000 ffff888098e8c040 0000000100000007 0000000000000000
kobject: 'ax2' (000000006eb79fe8): kobject_add_internal: parent: 'net', set: 'devices'
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888098e8cc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888098e8cd00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff888098e8cd80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff888098e8ce00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
mkiss: ax1: crc mode is auto.
 ffff888098e8ce80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================