TCP: request_sock_TCPv6: Possible SYN flooding on port 20030. Sending cookies.  Check SNMP counters.
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BUG: KASAN: use-after-free in erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801ac93980b by task syz-executor3/30218

CPU: 1 PID: 30218 Comm: syz-executor3 Not tainted 4.15.0+ #198
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+0x194/0x257 lib/dump_stack.c:53
 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_load_n_noabort+0xf/0x20 mm/kasan/report.c:440
 erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
 erspan_xmit+0x3b8/0x13b0 net/ipv4/ip_gre.c:740
 __netdev_start_xmit include/linux/netdevice.h:4042 [inline]
 netdev_start_xmit include/linux/netdevice.h:4051 [inline]
 packet_direct_xmit+0x315/0x6b0 net/packet/af_packet.c:266
 packet_snd net/packet/af_packet.c:2943 [inline]
 packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2968
 sock_sendmsg_nosec net/socket.c:638 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:648
 SYSC_sendto+0x361/0x5c0 net/socket.c:1729
 SyS_sendto+0x40/0x50 net/socket.c:1697
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
RIP: 0023:0xf7fb4c79
RSP: 002b:00000000f77b008c EFLAGS: 00000296 ORIG_RAX: 0000000000000171
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000020015f41
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020015fec
RBP: 0000000000000014 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0006b24e40 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 0000000100000001 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801ac939700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801ac939780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8801ac939800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff8801ac939880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801ac939900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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