==================================================================
BUG: KASAN: use-after-free in erspan_xmit+0x22d4/0x2430 net/ipv4/ip_gre.c:735
Read of size 2 at addr ffff8801d3c7b5cb by task syz-executor2/19213

CPU: 1 PID: 19213 Comm: syz-executor2 Not tainted 4.15.0-rc9+ #206
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_xmit+0x22d4/0x2430 net/ipv4/ip_gre.c:735
 __netdev_start_xmit include/linux/netdevice.h:4055 [inline]
 netdev_start_xmit include/linux/netdevice.h:4064 [inline]
 packet_direct_xmit+0x3ad/0x790 net/packet/af_packet.c:267
 packet_snd net/packet/af_packet.c:2944 [inline]
 packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2969
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:640
 SYSC_sendto+0x361/0x5c0 net/socket.c:1721
 SyS_sendto+0x40/0x50 net/socket.c:1689
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452f19
RSP: 002b:00007ff06b73bc58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452f19
RDX: 0000000000000000 RSI: 000000002000b000 RDI: 0000000000000013
RBP: 000000000000059c R08: 0000000020008000 R09: 000000000000001c
R10: 00000000000000c0 R11: 0000000000000212 R12: 00000000006f7740
R13: 00000000ffffffff R14: 00007ff06b73c6d4 R15: 0000000000000000

Allocated by task 3895:
 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
 mm_alloc+0x1d/0xd0 kernel/fork.c:889
 bprm_mm_init fs/exec.c:409 [inline]
 do_execveat_common.isra.30+0xba6/0x23c0 fs/exec.c:1771
 do_execve fs/exec.c:1847 [inline]
 SYSC_execve fs/exec.c:1928 [inline]
 SyS_execve+0x39/0x50 fs/exec.c:1923
 do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
 return_from_SYSCALL_64+0x0/0x75

Freed by task 3705:
 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
 __mmdrop+0x242/0x3d0 kernel/fork.c:911
 mmdrop include/linux/sched/mm.h:43 [inline]
 finish_task_switch+0x459/0x740 kernel/sched/core.c:2671
 context_switch kernel/sched/core.c:2802 [inline]
 __schedule+0x8f3/0x2060 kernel/sched/core.c:3375
 schedule+0xf5/0x430 kernel/sched/core.c:3434
 do_wait+0x33a/0xa70 kernel/exit.c:1540
 kernel_wait4+0x1f5/0x370 kernel/exit.c:1665
 SYSC_wait4+0x134/0x140 kernel/exit.c:1677
 SyS_wait4+0x2c/0x40 kernel/exit.c:1673
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801d3c7b340
 which belongs to the cache mm_struct of size 1440
The buggy address is located 651 bytes inside of
 1440-byte region [ffff8801d3c7b340, ffff8801d3c7b8e0)
The buggy address belongs to the page:
page:ffffea00074f1e80 count:1 mapcount:0 mapping:ffff8801d3c7a080 index:0xffff8801d3c7a080 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d3c7a080 ffff8801d3c7a080 0000000100000002
raw: ffffea00074fc6a0 ffffea0007514ea0 ffff8801dae279c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d3c7b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d3c7b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d3c7b580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8801d3c7b600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d3c7b680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================