==================================================================
BUG: KASAN: use-after-free in __write_once_size include/linux/compiler.h:305 [inline]
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:648 [inline]
BUG: KASAN: use-after-free in detach_timer kernel/time/timer.c:791 [inline]
BUG: KASAN: use-after-free in detach_if_pending+0x557/0x610 kernel/time/timer.c:808
Write of size 8 at addr ffff8801d0f841c0 by task syz-executor5/7471

CPU: 1 PID: 7471 Comm: syz-executor5 Not tainted 4.14.0-rc1+ #91
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x24e/0x340 mm/kasan/report.c:409
 __asan_report_store8_noabort+0x17/0x20 mm/kasan/report.c:435
 __write_once_size include/linux/compiler.h:305 [inline]
 __hlist_del include/linux/list.h:648 [inline]
 detach_timer kernel/time/timer.c:791 [inline]
 detach_if_pending+0x557/0x610 kernel/time/timer.c:808
 try_to_del_timer_sync+0xa2/0x120 kernel/time/timer.c:1182
 del_timer_sync+0x18a/0x240 kernel/time/timer.c:1247
 tun_flow_uninit drivers/net/tun.c:1104 [inline]
 tun_free_netdev+0x105/0x1b0 drivers/net/tun.c:1776
 netdev_run_todo+0x870/0xca0 net/core/dev.c:7864
 rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:106
 tun_detach drivers/net/tun.c:588 [inline]
 tun_chr_close+0x49/0x60 drivers/net/tun.c:2609
 __fput+0x333/0x7f0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x199/0x270 kernel/task_work.c:112
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0xa52/0x1b40 kernel/exit.c:865
 do_group_exit+0x149/0x400 kernel/exit.c:968
 get_signal+0x7e8/0x17e0 kernel/signal.c:2334
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x224/0x300 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath+0x42f/0x500 arch/x86/entry/common.c:266
 entry_SYSCALL_64_fastpath+0xbc/0xbe
RIP: 0033:0x4520a9
RSP: 002b:00007fa2b7a80c08 EFLAGS: 00000216 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffea RBX: 00000000007180b0 RCX: 00000000004520a9
RDX: 000000002077cfd8 RSI: 00000000400454ca RDI: 0000000000000027
RBP: 00000000000032b0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 00000000004b9aa0
R13: 00000000ffffffff R14: 0000000000000027 R15: 00000000400454ca

Allocated by task 7447:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 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
 __do_kmalloc_node mm/slab.c:3689 [inline]
 __kmalloc_node+0x47/0x70 mm/slab.c:3696
 kmalloc_node include/linux/slab.h:535 [inline]
 kvmalloc_node+0x64/0xd0 mm/util.c:397
 kvmalloc include/linux/mm.h:529 [inline]
 kvzalloc include/linux/mm.h:537 [inline]
 alloc_netdev_mqs+0x16e/0xed0 net/core/dev.c:8018
 tun_set_iff drivers/net/tun.c:2022 [inline]
 __tun_chr_ioctl+0x12be/0x3d20 drivers/net/tun.c:2276
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2521
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 7447:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 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:3503 [inline]
 kfree+0xca/0x250 mm/slab.c:3820
 kvfree+0x36/0x60 mm/util.c:416
 netdev_freemem net/core/dev.c:7970 [inline]
 free_netdev+0x2cf/0x360 net/core/dev.c:8132
 tun_set_iff drivers/net/tun.c:2105 [inline]
 __tun_chr_ioctl+0x2cf6/0x3d20 drivers/net/tun.c:2276
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2521
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe

The buggy address belongs to the object at ffff8801d0f80dc0
 which belongs to the cache kmalloc-16384 of size 16384
The buggy address is located 13312 bytes inside of
 16384-byte region [ffff8801d0f80dc0, ffff8801d0f84dc0)
The buggy address belongs to the page:
page:ffffea000743e000 count:1 mapcount:0 mapping:ffff8801d0f80dc0 index:0x0 compound_mapcount: 0
flags: 0x200000000008100(slab|head)
raw: 0200000000008100 ffff8801d0f80dc0 0000000000000000 0000000100000001
raw: ffffea00073cb620 ffffea00073c4220 ffff8801dac02200 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d0f84080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0f84100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d0f84180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff8801d0f84200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0f84280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================