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BUG: KASAN: use-after-free in free_netdev+0x3fb/0x480 net/core/dev.c:10045
Read of size 8 at addr ffff8880909286f8 by task syz-executor.0/12696

CPU: 1 PID: 12696 Comm: syz-executor.0 Not tainted 5.8.0-rc3-next-20200703-syzkaller #0
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+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 free_netdev+0x3fb/0x480 net/core/dev.c:10045
 netdev_run_todo+0x88e/0xac0 net/core/dev.c:9797
 rtnl_unlock net/core/rtnetlink.c:112 [inline]
 rtnetlink_rcv_msg+0x45b/0xad0 net/core/rtnetlink.c:5461
 netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2469
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2352
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2406
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:367
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45cb29
Code: Bad RIP value.
RSP: 002b:00007fd41d6c5c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000502760 RCX: 000000000045cb29
RDX: 0000000000000000 RSI: 0000000020000140 RDI: 0000000000000005
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000a43 R14: 00000000004cd2a1 R15: 00007fd41d6c66d4

Allocated by task 12696:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:494
 __do_kmalloc mm/slab.c:3659 [inline]
 __kmalloc+0x18f/0x4d0 mm/slab.c:3668
 kmalloc include/linux/slab.h:559 [inline]
 sk_prot_alloc+0x17a/0x300 net/core/sock.c:1684
 sk_alloc+0x32/0xbd0 net/core/sock.c:1738
 tun_chr_open+0x7b/0x540 drivers/net/tun.c:3387
 misc_open+0x372/0x4a0 drivers/char/misc.c:141
 chrdev_open+0x266/0x770 fs/char_dev.c:414
 do_dentry_open+0x4b9/0x11b0 fs/open.c:822
 do_open fs/namei.c:3249 [inline]
 path_openat+0x1bb9/0x2750 fs/namei.c:3366
 do_filp_open+0x17e/0x3c0 fs/namei.c:3393
 do_sys_openat2+0x16f/0x3b0 fs/open.c:1173
 do_sys_open fs/open.c:1189 [inline]
 __do_sys_openat fs/open.c:1203 [inline]
 __se_sys_openat fs/open.c:1198 [inline]
 __x64_sys_openat+0x13f/0x1f0 fs/open.c:1198
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:367
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 12690:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf2/0x130 mm/kasan/common.c:455
 __cache_free mm/slab.c:3422 [inline]
 kfree+0x103/0x2c0 mm/slab.c:3760
 sk_prot_free net/core/sock.c:1721 [inline]
 __sk_destruct+0x63b/0x860 net/core/sock.c:1806
 sk_destruct+0xbd/0xe0 net/core/sock.c:1821
 __sk_free+0xef/0x3d0 net/core/sock.c:1832
 sk_free+0x78/0xa0 net/core/sock.c:1843
 sock_put include/net/sock.h:1789 [inline]
 __tun_detach+0xd69/0x1310 drivers/net/tun.c:696
 tun_detach drivers/net/tun.c:708 [inline]
 tun_chr_close+0x10e/0x180 drivers/net/tun.c:3423
 __fput+0x33c/0x880 fs/file_table.c:281
 task_work_run+0xdd/0x190 kernel/task_work.c:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:222 [inline]
 __prepare_exit_to_usermode+0x1e9/0x1f0 arch/x86/entry/common.c:252
 do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:376
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff888090928000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1784 bytes inside of
 4096-byte region [ffff888090928000, ffff888090929000)
The buggy address belongs to the page:
page:ffffea0002424a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 head:ffffea0002424a00 order:1 compound_mapcount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea0001f1fb88 ffffea0002572588 ffff8880aa000900
raw: 0000000000000000 ffff888090928000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888090928580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888090928600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888090928680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff888090928700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888090928780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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