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BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:188 [inline]
BUG: KASAN: use-after-free in sk_dst_get include/net/sock.h:1768 [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 ffff8801d0935228 by task syzkaller781639/5598

CPU: 0 PID: 5598 Comm: syzkaller781639 Not tainted 4.15.0-rc8-next-20180117+ #99
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:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 __read_once_size include/linux/compiler.h:188 [inline]
 sk_dst_get include/net/sock.h:1768 [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:00007fff31c16ff8 EFLAGS: 00000207 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000440879
RDX: 000000000000002e RSI: 00000000205fafd2 RDI: 0000000000000004
RBP: 0000000000009596 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000207 R12: 0000000000000000
R13: 0000000000401d70 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 5594:
 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:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
 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 5598:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x86/0x2b0 mm/slab.c:3743
 sk_prot_free net/core/sock.c:1506 [inline]
 __sk_destruct+0x628/0x920 net/core/sock.c:1590
 __rcu_reclaim kernel/rcu/rcu.h:172 [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+0xd6c/0x17f0 kernel/rcu/tree.c:2917
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801d0935000
 which belongs to the cache UDPv6 of size 1664
The buggy address is located 552 bytes inside of
 1664-byte region [ffff8801d0935000, ffff8801d0935680)
The buggy address belongs to the page:
page:ffffea0007424d40 count:1 mapcount:0 mapping:ffff8801d0935000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d0935000 0000000000000000 0000000100000002
raw: ffffea0007438a20 ffffea0007223ce0 ffff8801d32c49c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d0935100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0935180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d0935200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801d0935280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0935300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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