audit: type=1326 audit(1517351839.511:634): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=14824 comm="syz-executor5" exe="/root/syz-executor5" sig=0 arch=c000003e syscall=257 compat=0 ip=0x453299 code=0x7ffc0000
==================================================================
BUG: KASAN: use-after-free in l2tp_session_create+0xa6d/0xc60 net/l2tp/l2tp_core.c:1757
Read of size 4 at addr ffff8801ba5fd8e8 by task syz-executor2/14841

CPU: 0 PID: 14841 Comm: syz-executor2 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_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: 0033:0x453299
RSP: 002b:00007ff877da9c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000453299
RDX: 000000000000002e RSI: 00000000205fafd2 RDI: 000000000000001a
RBP: 00000000000005d5 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f7c98
R13: 00000000ffffffff R14: 00007ff877daa6d4 R15: 0000000000000000

Allocated by task 14841:
 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 16:
 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:167 [inline]
 rcu_do_batch kernel/rcu/tree.c:2674 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2933 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2900 [inline]
 rcu_process_callbacks+0xe94/0x17f0 kernel/rcu/tree.c:2917
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801ba5fd800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 232 bytes inside of
 512-byte region [ffff8801ba5fd800, ffff8801ba5fda00)
The buggy address belongs to the page:
page:ffffea0006e97f40 count:1 mapcount:0 mapping:ffff8801ba5fd080 index:0xffff8801ba5fda80
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801ba5fd080 ffff8801ba5fda80 0000000100000004
raw: ffffea0006ed7e20 ffffea000729c960 ffff8801db000940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801ba5fd780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801ba5fd800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801ba5fd880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8801ba5fd900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801ba5fd980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================