==================================================================
BUG: KASAN: use-after-free in erspan_build_header+0x392/0x3b0 net/ipv4/ip_gre.c:706
Read of size 2 at addr ffff88807b19f28b by task syz-executor.3/26377

CPU: 1 PID: 26377 Comm: syz-executor.3 Not tainted 4.14.115 #5
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+0x138/0x19c lib/dump_stack.c:53
 print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0x11e/0x2db mm/kasan/report.c:393
 __asan_report_load_n_noabort+0xf/0x20 mm/kasan/report.c:440
 erspan_build_header+0x392/0x3b0 net/ipv4/ip_gre.c:706
 erspan_xmit net/ipv4/ip_gre.c:748 [inline]
 erspan_xmit+0x3ec/0x11c0 net/ipv4/ip_gre.c:725
 __netdev_start_xmit include/linux/netdevice.h:4033 [inline]
 netdev_start_xmit include/linux/netdevice.h:4042 [inline]
 packet_direct_xmit+0x438/0x640 net/packet/af_packet.c:269
 packet_snd net/packet/af_packet.c:2969 [inline]
 packet_sendmsg+0x31e1/0x5990 net/packet/af_packet.c:2994
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xd0/0x110 net/socket.c:656
 ___sys_sendmsg+0x70c/0x850 net/socket.c:2062
 __sys_sendmsg+0xb9/0x140 net/socket.c:2096
 SYSC_sendmsg net/socket.c:2107 [inline]
 SyS_sendmsg+0x2d/0x50 net/socket.c:2103
 do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x458da9
RSP: 002b:00007f5385d7cc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458da9
RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5385d7d6d4
R13: 00000000004c6636 R14: 00000000004daf58 R15: 00000000ffffffff

Allocated by task 25315:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 kasan_slab_alloc+0xf/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x780 mm/slab.c:3552
 getname_flags fs/namei.c:138 [inline]
 getname_flags+0xcb/0x580 fs/namei.c:128
 getname+0x1a/0x20 fs/namei.c:209
 do_sys_open+0x1e7/0x430 fs/open.c:1059
 SYSC_open fs/open.c:1083 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1078
 do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 25315:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kmem_cache_free+0x83/0x2b0 mm/slab.c:3758
 putname+0xdb/0x120 fs/namei.c:259
 do_sys_open+0x21c/0x430 fs/open.c:1074
 SYSC_open fs/open.c:1083 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1078
 do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88807b19ed40
 which belongs to the cache names_cache of size 4096
The buggy address is located 1355 bytes inside of
 4096-byte region [ffff88807b19ed40, ffff88807b19fd40)
The buggy address belongs to the page:
page:ffffea0001ec6780 count:1 mapcount:0 mapping:ffff88807b19ed40 index:0x0 compound_mapcount: 0
flags: 0x1fffc0000008100(slab|head)
raw: 01fffc0000008100 ffff88807b19ed40 0000000000000000 0000000100000001
raw: ffffea00025f31a0 ffffea000141eba0 ffff8880aa9e0cc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88807b19f180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b19f200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807b19f280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88807b19f300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b19f380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
kobject: 'loop4' (ffff8880a4aa8120): fill_kobj_path: path = '/devices/virtual/block/loop4'