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BUG: KASAN: slab-out-of-bounds in erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801d9b2dccb by task syz-executor1/22798

CPU: 1 PID: 22798 Comm: syz-executor1 Not tainted 4.15.0+ #287
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
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x453299
RSP: 002b:00007f21cb0b6c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000453299
RDX: 0000000000000000 RSI: 0000000020015f41 RDI: 0000000000000013
RBP: 00000000000005e0 R08: 0000000020015fec R09: 0000000000000014
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f7da0
R13: 00000000ffffffff R14: 00007f21cb0b76d4 R15: 0000000000000000

Allocated by task 4215:
 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:3708 [inline]
 __kmalloc_track_caller+0x15e/0x760 mm/slab.c:3723
 kmemdup+0x24/0x50 mm/util.c:118
 kmemdup include/linux/string.h:417 [inline]
 __addrconf_sysctl_register+0xae/0x400 net/ipv6/addrconf.c:6381
 addrconf_sysctl_register+0x116/0x1b0 net/ipv6/addrconf.c:6446
 ipv6_add_dev+0xa3d/0x12f0 net/ipv6/addrconf.c:458
 addrconf_notify+0x861/0x2270 net/ipv6/addrconf.c:3380
 notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 call_netdevice_notifiers_info+0x32/0x60 net/core/dev.c:1691
 call_netdevice_notifiers net/core/dev.c:1709 [inline]
 register_netdevice+0xd2a/0x1010 net/core/dev.c:7750
 register_netdev+0x1a/0x30 net/core/dev.c:7835
 ip6gre_init_net+0x3b1/0x640 net/ipv6/ip6_gre.c:1180
 ops_init+0x10a/0x570 net/core/net_namespace.c:118
 setup_net+0x313/0x710 net/core/net_namespace.c:295
 copy_net_ns+0x27c/0x580 net/core/net_namespace.c:419
 create_new_namespaces+0x425/0x880 kernel/nsproxy.c:107
 unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:206
 SYSC_unshare kernel/fork.c:2365 [inline]
 SyS_unshare+0x653/0xfa0 kernel/fork.c:2315
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801d9b2c900
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 971 bytes to the right of
 4096-byte region [ffff8801d9b2c900, ffff8801d9b2d900)
The buggy address belongs to the page:
page:ffffea000766cb00 count:1 mapcount:0 mapping:ffff8801d9b2c900 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d9b2c900 0000000000000000 0000000100000001
raw: ffffea0006b103a0 ffffea000766f920 ffff8801db000dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d9b2db80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d9b2dc00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d9b2dc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                              ^
 ffff8801d9b2dd00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d9b2dd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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