==================================================================
BUG: KASAN: use-after-free in erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801bcfdbb0b by task syz-executor2/5373

CPU: 0 PID: 5373 Comm: syz-executor2 Not tainted 4.15.0-rc9+ #284
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:00007fdb1a297c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000453299
RDX: 00000000000000b4 RSI: 0000000020011f4c RDI: 0000000000000013
RBP: 00000000000003d6 R08: 0000000020008000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4cb0
R13: 00000000ffffffff R14: 00007fdb1a2986d4 R15: 0000000000000000

Allocated by task 3890:
 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
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3544
 kmem_cache_zalloc include/linux/slab.h:678 [inline]
 copy_signal+0xfe/0xa11 kernel/fork.c:1396
 copy_process.part.38+0x1ed2/0x4b20 kernel/fork.c:1749
 copy_process kernel/fork.c:1565 [inline]
 _do_fork+0x1f7/0xfe0 kernel/fork.c:2044
 SYSC_clone kernel/fork.c:2154 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2148
 do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
 return_from_SYSCALL_64+0x0/0x75

Freed by task 3896:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3488 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3746
 free_signal_struct kernel/fork.c:403 [inline]
 put_signal_struct kernel/fork.c:409 [inline]
 __put_task_struct+0x33f/0x580 kernel/fork.c:423
 put_task_struct include/linux/sched/task.h:96 [inline]
 delayed_put_task_struct+0xca/0x3d0 kernel/exit.c:180
 __rcu_reclaim kernel/rcu/rcu.h:195 [inline]
 rcu_do_batch kernel/rcu/tree.c:2758 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
 rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2996
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801bcfdb700
 which belongs to the cache signal_cache of size 1296
The buggy address is located 1035 bytes inside of
 1296-byte region [ffff8801bcfdb700, ffff8801bcfdbc10)
The buggy address belongs to the page:
page:ffffea0006f3f680 count:1 mapcount:0 mapping:ffff8801bcfda000 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bcfda000 0000000000000000 0000000100000005
raw: ffffea00070bfda0 ffffea0007653220 ffff8801dae28e40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bcfdba00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bcfdba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801bcfdbb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8801bcfdbb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bcfdbc00: fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================