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BUG: KASAN: use-after-free in __list_add_valid+0xb1/0xd0 lib/list_debug.c:23
Read of size 8 at addr ffff8801c9f1c968 by task syz-executor7/6690

CPU: 1 PID: 6690 Comm: syz-executor7 Not tainted 4.14.0-rc5-next-20171018+ #36
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+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 __list_add_valid+0xb1/0xd0 lib/list_debug.c:23
 __list_add include/linux/list.h:59 [inline]
 list_add include/linux/list.h:78 [inline]
 netif_napi_add+0x299/0x980 net/core/dev.c:5532
 tun_napi_init drivers/net/tun.c:280 [inline]
 tun_attach+0xbc0/0x1080 drivers/net/tun.c:764
 tun_set_iff drivers/net/tun.c:2205 [inline]
 __tun_chr_ioctl+0x209d/0x3e50 drivers/net/tun.c:2502
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2747
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1520 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
RIP: 0033:0x452719
RSP: 002b:00007f492c532be8 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000758020 RCX: 0000000000452719
RDX: 00000000204c8fd8 RSI: 00000000400454ca RDI: 0000000000000018
RBP: 0000000000000082 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4478
R13: 00000000ffffffff R14: 00007f492c5336d4 R15: 0000000000000000

Allocated by task 6690:
 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 mm/slab.c:3712 [inline]
 __kmalloc+0x162/0x760 mm/slab.c:3721
 kmalloc include/linux/slab.h:507 [inline]
 sk_prot_alloc+0x101/0x2a0 net/core/sock.c:1469
 sk_alloc+0x89/0x700 net/core/sock.c:1523
 tun_chr_open+0xec/0x490 drivers/net/tun.c:2804
 misc_open+0x382/0x500 drivers/char/misc.c:153
 chrdev_open+0x257/0x730 fs/char_dev.c:416
 do_dentry_open+0x664/0xd40 fs/open.c:752
 vfs_open+0x107/0x220 fs/open.c:866
 do_last fs/namei.c:3387 [inline]
 path_openat+0x1151/0x3520 fs/namei.c:3527
 do_filp_open+0x25b/0x3b0 fs/namei.c:3562
 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/0xbe

Freed by task 6690:
 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:3492 [inline]
 kfree+0xca/0x250 mm/slab.c:3807
 sk_prot_free net/core/sock.c:1506 [inline]
 __sk_destruct+0x74a/0x910 net/core/sock.c:1585
 sk_destruct+0x47/0x80 net/core/sock.c:1593
 __sk_free+0x57/0x230 net/core/sock.c:1601
 sk_free+0x2a/0x40 net/core/sock.c:1612
 sock_put include/net/sock.h:1651 [inline]
 __tun_detach+0x75b/0x1570 drivers/net/tun.c:657
 tun_detach drivers/net/tun.c:664 [inline]
 tun_chr_close+0x44/0x60 drivers/net/tun.c:2835
 __fput+0x327/0x7e0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x199/0x270 kernel/task_work.c:112
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath+0x42f/0x510 arch/x86/entry/common.c:266
 entry_SYSCALL_64_fastpath+0xbc/0xbe

The buggy address belongs to the object at ffff8801c9f1c3c0
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1448 bytes inside of
 2048-byte region [ffff8801c9f1c3c0, ffff8801c9f1cbc0)
The buggy address belongs to the page:
page:ffffea000727c700 count:1 mapcount:0 mapping:ffff8801c9f1c3c0 index:0x0 compound_mapcount: 0
flags: 0x200000000008100(slab|head)
raw: 0200000000008100 ffff8801c9f1c3c0 0000000000000000 0000000100000003
raw: ffffea00072ac3a0 ffffea0007259120 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c9f1c800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c9f1c880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c9f1c900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8801c9f1c980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c9f1ca00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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