==================================================================
BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:183 [inline]
BUG: KASAN: use-after-free in sk_dst_get include/net/sock.h:1766 [inline]
BUG: KASAN: use-after-free in pppol2tp_session_init net/l2tp/l2tp_ppp.c:596 [inline]
BUG: KASAN: use-after-free in pppol2tp_connect+0x1a91/0x1dd0 net/l2tp/l2tp_ppp.c:756
Read of size 8 at addr ffff8801d7d30ae8 by task syzkaller636167/4198

CPU: 1 PID: 4198 Comm: syzkaller636167 Not tainted 4.15.0-rc8+ #202
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_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 __read_once_size include/linux/compiler.h:183 [inline]
 sk_dst_get include/net/sock.h:1766 [inline]
 pppol2tp_session_init net/l2tp/l2tp_ppp.c:596 [inline]
 pppol2tp_connect+0x1a91/0x1dd0 net/l2tp/l2tp_ppp.c:756
 SYSC_connect+0x213/0x4a0 net/socket.c:1613
 SyS_connect+0x24/0x30 net/socket.c:1594
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x440879
RSP: 002b:00007ffc757de308 EFLAGS: 00000207 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000440879
RDX: 000000000000002e RSI: 00000000205fafd2 RDI: 0000000000000004
RBP: 0000000000006caa R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000207 R12: 0000000000000000
R13: 0000000000401d70 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4194:
 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
 sk_prot_alloc+0x65/0x2a0 net/core/sock.c:1465
 sk_alloc+0x105/0x1440 net/core/sock.c:1525
 inet6_create+0x44d/0x10f0 net/ipv6/af_inet6.c:183
 __sock_create+0x4d4/0x850 net/socket.c:1259
 sock_create net/socket.c:1299 [inline]
 SYSC_socket net/socket.c:1329 [inline]
 SyS_socket+0xeb/0x1d0 net/socket.c:1309
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 4198:
 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
 sk_prot_free net/core/sock.c:1506 [inline]
 __sk_destruct+0x628/0x920 net/core/sock.c:1590
 __rcu_reclaim kernel/rcu/rcu.h:195 [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+0xd6c/0x17f0 kernel/rcu/tree.c:2996
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801d7d308c0
 which belongs to the cache UDPv6 of size 1664
The buggy address is located 552 bytes inside of
 1664-byte region [ffff8801d7d308c0, ffff8801d7d30f40)
The buggy address belongs to the page:
page:ffffea00075f4c00 count:1 mapcount:0 mapping:ffff8801d7d301c0 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d7d301c0 0000000000000000 0000000100000002
raw: ffffea00076069e0 ffffea000760b420 ffff8801d32e3cc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d7d30980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d7d30a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d7d30a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8801d7d30b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d7d30b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================