TCP: request_sock_TCP: Possible SYN flooding on port 20026. Sending cookies.  Check SNMP counters.
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BUG: KASAN: use-after-free in l2tp_session_create+0xa6d/0xc60 net/l2tp/l2tp_core.c:1757
Read of size 4 at addr ffff8801c1c098a8 by task syz-executor5/7746

CPU: 0 PID: 7746 Comm: syz-executor5 Not tainted 4.15.0-rc9+ #278
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_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 l2tp_session_create+0xa6d/0xc60 net/l2tp/l2tp_core.c:1757
 pppol2tp_connect+0xed7/0x1dd0 net/l2tp/l2tp_ppp.c:748
 SYSC_connect+0x213/0x4a0 net/socket.c:1621
 SyS_connect+0x24/0x30 net/socket.c:1602
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452f19
RSP: 002b:00007f5a03274c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452f19
RDX: 0000000000000032 RSI: 0000000020e71000 RDI: 0000000000000014
RBP: 00000000000005d4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f7c80
R13: 00000000ffffffff R14: 00007f5a032756d4 R15: 0000000000000000

Allocated by task 7746:
 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
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610
 kmalloc include/linux/slab.h:499 [inline]
 kzalloc include/linux/slab.h:688 [inline]
 l2tp_tunnel_create+0x5e1/0x17f0 net/l2tp/l2tp_core.c:1554
 pppol2tp_connect+0x14b7/0x1dd0 net/l2tp/l2tp_ppp.c:707
 SYSC_connect+0x213/0x4a0 net/socket.c:1621
 SyS_connect+0x24/0x30 net/socket.c:1602
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 7752:
 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]
 kfree+0xd6/0x260 mm/slab.c:3803
 __rcu_reclaim kernel/rcu/rcu.h:190 [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+0xe94/0x17f0 kernel/rcu/tree.c:2996
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801c1c097c0
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 232 bytes inside of
 512-byte region [ffff8801c1c097c0, ffff8801c1c099c0)
The buggy address belongs to the page:
page:ffffea0007070240 count:1 mapcount:0 mapping:ffff8801c1c09040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c1c09040 0000000000000000 0000000100000006
raw: ffffea000708ffe0 ffffea0007073ba0 ffff8801dac00940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c1c09780: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8801c1c09800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c1c09880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801c1c09900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c1c09980: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
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