==================================================================
BUG: KASAN: use-after-free in l2tp_session_create+0x1339/0x1600 net/l2tp/l2tp_core.c:1799
Read of size 4 at addr ffff8880a95fe868 by task syz-executor.0/7755

CPU: 1 PID: 7755 Comm: syz-executor.0 Not tainted 4.14.146 #0
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+0x138/0x197 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+0xa9/0x2af mm/kasan/report.c:393
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 l2tp_session_create+0x1339/0x1600 net/l2tp/l2tp_core.c:1799
 pppol2tp_connect+0x11bf/0x18b0 net/l2tp/l2tp_ppp.c:721
 SYSC_connect+0x1f6/0x2d0 net/socket.c:1655
 SyS_connect+0x24/0x30 net/socket.c:1636
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459a29
RSP: 002b:00007efec8380c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a29
RDX: 0000000000000026 RSI: 0000000020000180 RDI: 0000000000000005
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007efec83816d4
R13: 00000000004bff90 R14: 00000000004d1f00 R15: 00000000ffffffff

Allocated by task 7755:
 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
 kmem_cache_alloc_trace+0x152/0x790 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 l2tp_tunnel_create+0x3d4/0xd90 net/l2tp/l2tp_core.c:1607
 pppol2tp_connect+0x116b/0x18b0 net/l2tp/l2tp_ppp.c:677
 SYSC_connect+0x1f6/0x2d0 net/socket.c:1655
 SyS_connect+0x24/0x30 net/socket.c:1636
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 7:
 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]
 kfree+0xcc/0x270 mm/slab.c:3815
 __rcu_reclaim kernel/rcu/rcu.h:190 [inline]
 rcu_do_batch kernel/rcu/tree.c:2699 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2962 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2929 [inline]
 rcu_process_callbacks+0x8d0/0x12b0 kernel/rcu/tree.c:2946
 __do_softirq+0x244/0x9a0 kernel/softirq.c:288

The buggy address belongs to the object at ffff8880a95fe780
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 232 bytes inside of
 512-byte region [ffff8880a95fe780, ffff8880a95fe980)
The buggy address belongs to the page:
page:ffffea0002a57f80 count:1 mapcount:0 mapping:ffff8880a95fe000 index:0x0
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff8880a95fe000 0000000000000000 0000000100000006
raw: ffffea0002a5e160 ffffea00022682a0 ffff8880aa800940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a95fe700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880a95fe780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a95fe800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8880a95fe880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a95fe900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
kobject: 'kvm' (ffff888219f93590): fill_kobj_path: path = '/devices/virtual/misc/kvm'