==================================================================
BUG: KASAN: use-after-free in sock_net_uid include/net/sock.h:1733 [inline]
BUG: KASAN: use-after-free in ip6_route_me_harder+0x9d8/0xc00 net/ipv6/netfilter.c:26
Read of size 4 at addr ffff8801cd82c1b0 by task syz-executor5/21161

CPU: 1 PID: 21161 Comm: syz-executor5 Not tainted 4.16.0-rc2+ #251
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 sock_net_uid include/net/sock.h:1733 [inline]
 ip6_route_me_harder+0x9d8/0xc00 net/ipv6/netfilter.c:26
 nf_nat_ipv6_local_fn+0x2a4/0x5d0 net/ipv6/netfilter/nf_nat_l3proto_ipv6.c:414
 ip6table_nat_local_fn+0x2c/0x40 net/ipv6/netfilter/ip6table_nat.c:69
 nf_hook_entry_hookfn include/linux/netfilter.h:120 [inline]
 nf_hook_slow+0xba/0x1a0 net/netfilter/core.c:483
 nf_hook include/linux/netfilter.h:243 [inline]
 NF_HOOK include/linux/netfilter.h:286 [inline]
 ip6_xmit+0x10f5/0x2260 net/ipv6/ip6_output.c:277
 tcp_v6_send_synack+0x57b/0xaa0 net/ipv6/tcp_ipv6.c:490
 tcp_conn_request+0x26fd/0x3660 net/ipv4/tcp_input.c:6335
 tcp_v6_conn_request+0x212/0x270 net/ipv6/tcp_ipv6.c:1021
 tcp_rcv_state_process+0x92a/0x4760 net/ipv4/tcp_input.c:5842
 tcp_v6_do_rcv+0x739/0x1250 net/ipv6/tcp_ipv6.c:1331
 tcp_v6_rcv+0x25a0/0x2d40 net/ipv6/tcp_ipv6.c:1521
 ip6_input_finish+0x37e/0x17a0 net/ipv6/ip6_input.c:284
 NF_HOOK include/linux/netfilter.h:288 [inline]
 ip6_input+0xdb/0x560 net/ipv6/ip6_input.c:327
 dst_input include/net/dst.h:449 [inline]
 ip6_rcv_finish+0x297/0x8c0 net/ipv6/ip6_input.c:71
 NF_HOOK include/linux/netfilter.h:288 [inline]
 ipv6_rcv+0xf37/0x1fa0 net/ipv6/ip6_input.c:208
 __netif_receive_skb_core+0x1a41/0x3460 net/core/dev.c:4554
 __netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4619
 netif_receive_skb_internal+0x10b/0x670 net/core/dev.c:4693
 netif_receive_skb+0xae/0x390 net/core/dev.c:4717
 tun_rx_batched.isra.52+0x5ee/0x870 drivers/net/tun.c:1556
 tun_get_user+0x25a5/0x3810 drivers/net/tun.c:1957
 tun_chr_write_iter+0xbd/0x1c0 drivers/net/tun.c:1985
 call_write_iter include/linux/fs.h:1781 [inline]
 do_iter_readv_writev+0x55c/0x830 fs/read_write.c:653
 do_iter_write+0x154/0x540 fs/read_write.c:932
 vfs_writev+0x18a/0x340 fs/read_write.c:977
 do_writev+0xfc/0x2a0 fs/read_write.c:1012
 SYSC_writev fs/read_write.c:1085 [inline]
 SyS_writev+0x27/0x30 fs/read_write.c:1082
 do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x453c41
RSP: 002b:00007fbaafe05ba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 000000000000004a RCX: 0000000000453c41
RDX: 0000000000000001 RSI: 00007fbaafe05bf0 RDI: 00000000000000fc
RBP: 0000000020000100 R08: 00000000000000fc R09: 0000000000000000
R10: 000000000000004a R11: 0000000000000293 R12: 00000000ffffffff
R13: 0000000000000627 R14: 00000000006f9448 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0007360b00 count:0 mapcount:-127 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffff80
raw: ffffea00075e4520 ffffea00067b0c20 0000000000000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801cd82c080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801cd82c100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8801cd82c180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                     ^
 ffff8801cd82c200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801cd82c280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================