pktgen: kernel_thread() failed for cpu 0
pktgen: Cannot create thread for cpu 0 (-4)
pktgen: kernel_thread() failed for cpu 1
pktgen: Cannot create thread for cpu 1 (-4)
==================================================================
BUG: KASAN: use-after-free in l2tp_session_create+0x15d9/0x16f0 net/l2tp/l2tp_core.c:1911
Read of size 8 at addr ffff8801c522a900 by task syz-executor3/10389

CPU: 1 PID: 10389 Comm: syz-executor3 Not tainted 4.9.124-g09eb2ba #31
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff88019f887a20 ffffffff81eb95e9 ffffea0007148a80 ffff8801c522a900
 0000000000000000 ffff8801c522a900 ffff88019f887c78 ffff88019f887a58
 ffffffff8156c35e ffff8801c522a900 0000000000000008 0000000000000000
Call Trace:
 [<ffffffff81eb95e9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb95e9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8156c35e>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
 [<ffffffff8156c768>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<ffffffff8156c768>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
 [<ffffffff8153faf4>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 [<ffffffff836c9529>] l2tp_session_create+0x15d9/0x16f0 net/l2tp/l2tp_core.c:1911
 [<ffffffff836cdd67>] pppol2tp_connect+0x10d7/0x18f0 net/l2tp/l2tp_ppp.c:718
 [<ffffffff8301ea38>] SYSC_connect+0x1b8/0x300 net/socket.c:1575
 [<ffffffff83021314>] SyS_connect+0x24/0x30 net/socket.c:1556
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a019d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Allocated by task 10389:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:609
 kmem_cache_alloc_trace+0xfd/0x2b0 mm/slub.c:2742
 kmalloc include/linux/slab.h:490 [inline]
 kzalloc include/linux/slab.h:636 [inline]
 l2tp_tunnel_create+0x438/0x1070 net/l2tp/l2tp_core.c:1646
 pppol2tp_connect+0x1440/0x18f0 net/l2tp/l2tp_ppp.c:674
 SYSC_connect+0x1b8/0x300 net/socket.c:1575
 SyS_connect+0x24/0x30 net/socket.c:1556
 do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Freed by task 17:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582
 slab_free_hook mm/slub.c:1355 [inline]
 slab_free_freelist_hook mm/slub.c:1377 [inline]
 slab_free mm/slub.c:2958 [inline]
 kfree+0xfb/0x310 mm/slub.c:3878
 __rcu_reclaim kernel/rcu/rcu.h:113 [inline]
 rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 rcu_process_callbacks+0x9d5/0x12b0 kernel/rcu/tree.c:3037
 __do_softirq+0x210/0x940 kernel/softirq.c:288

The buggy address belongs to the object at ffff8801c522a780
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 384 bytes inside of
 512-byte region [ffff8801c522a780, ffff8801c522a980)
The buggy address belongs to the page:
page:ffffea0007148a80 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c522a800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c522a880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c522a900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801c522a980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c522aa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================