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BUG: KASAN: use-after-free in free_netdev+0x31a/0x360 net/core/dev.c:8192
Read of size 8 at addr ffff880020ef37a0 by task syz-executor6/5851

CPU: 3 PID: 5851 Comm: syz-executor6 Not tainted 4.14.0-rc5-next-20171018+ #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 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
 free_netdev+0x31a/0x360 net/core/dev.c:8192
 netdev_run_todo+0x736/0xae0 net/core/dev.c:7940
 rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:106
 tun_detach drivers/net/tun.c:665 [inline]
 tun_chr_close+0x49/0x60 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
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0x9b5/0x1ad0 kernel/exit.c:869
 do_group_exit+0x149/0x400 kernel/exit.c:972
 SYSC_exit_group kernel/exit.c:983 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:981
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x447c89
RSP: 002b:0000000000a5fa08 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000008529 RCX: 0000000000447c89
RDX: 0000000000447c89 RSI: 0000000000756150 RDI: 0000000000000000
RBP: 0000000000000082 R08: 000000000000001c R09: 0000000000000000
R10: 0000000000756148 R11: 0000000000000202 R12: 0000000000a5f9b0
R13: 0000000000748020 R14: 0000000000000588 R15: 000000000000001d

Allocated by task 5852:
 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 5851:
 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
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0x9b5/0x1ad0 kernel/exit.c:869
 do_group_exit+0x149/0x400 kernel/exit.c:972
 SYSC_exit_group kernel/exit.c:983 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:981
 entry_SYSCALL_64_fastpath+0x1f/0xbe

The buggy address belongs to the object at ffff880020ef3200
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1440 bytes inside of
 2048-byte region [ffff880020ef3200, ffff880020ef3a00)
The buggy address belongs to the page:
page:ffffea000083bc80 count:1 mapcount:0 mapping:ffff880020ef2100 index:0x0 compound_mapcount: 0
flags: 0x100000000008100(slab|head)
raw: 0100000000008100 ffff880020ef2100 0000000000000000 0000000100000003
raw: ffffea0000873620 ffffea0000876ea0 ffff88003e800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff880020ef3680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff880020ef3700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff880020ef3780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff880020ef3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff880020ef3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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