Subject: KASAN: use-after-free Read in pppol2tp_connect

From: syzbot <[email-masked]>
Date: Mon, 15 Jan 2018 19:58:01 -0800

Hello,

syzkaller hit the following crash on  
b625c1ff82272e26c76570d3c7123419ec345b20
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers

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Reported-by: [email-masked]
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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 ffff8801c2c402a8 by task syzkaller472056/4457

CPU: 0 PID: 4457 Comm: syzkaller472056 Not tainted  
4.15.0-rc7-next-20180115+ #97
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: 0033:0x445c69
RSP: 002b:00007f200cbabdb8 EFLAGS: 00000297 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00000000006dbc24 RCX: 0000000000445c69
RDX: 000000000000002e RSI: 00000000205fafd2 RDI: 0000000000000005
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000000000
R13: 00007ffc2560dabf R14: 00007f200cbac9c0 R15: 0000000000000005

Allocated by task 4454:
  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 4457:
  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+0x622/0x910 net/core/sock.c:1590
  sk_destruct+0x47/0x80 net/core/sock.c:1598
  __sk_free+0xf1/0x2b0 net/core/sock.c:1609
  sk_free+0x2a/0x40 net/core/sock.c:1620
  sock_put include/net/sock.h:1660 [inline]
  l2tp_session_free+0x21c/0x2b0 net/l2tp/l2tp_core.c:1665
  l2tp_session_dec_refcount net/l2tp/l2tp_core.h:302 [inline]
  pppol2tp_session_destruct+0xd4/0x110 net/l2tp/l2tp_ppp.c:448
  __sk_destruct+0xfd/0x910 net/core/sock.c:1563
  sk_destruct+0x47/0x80 net/core/sock.c:1598
  __sk_free+0xf1/0x2b0 net/core/sock.c:1609
  sk_free+0x2a/0x40 net/core/sock.c:1620
  sock_put include/net/sock.h:1660 [inline]
  pppol2tp_put_sk+0x49/0x60 net/l2tp/l2tp_ppp.c:457
  __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 ffff8801c2c40080
  which belongs to the cache UDPv6 of size 1664
The buggy address is located 552 bytes inside of
  1664-byte region [ffff8801c2c40080, ffff8801c2c40700)
The buggy address belongs to the page:
page:ffffea00070b1000 count:1 mapcount:0 mapping:ffff8801c2c40080 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c2c40080 0000000000000000 0000000100000002
raw: ffffea0007624fe0 ffffea000760c820 ffff8801d3379840 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801c2c40180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801c2c40200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801c2c40280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                   ^
  ffff8801c2c40300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801c2c40380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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