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

From: syzbot <[email-masked]>
Date: Sat, 09 Dec 2017 12:50:01 -0800

Hello,

syzkaller hit the following crash on  
82bcf1def3b5f1251177ad47c44f7e17af039b4b
git://git.cmpxchg.org/linux-mmots.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

Unfortunately, I don't have any reproducer for this bug yet.

==================================================================
BUG: KASAN: use-after-free in inet_create+0xda0/0xf50 net/ipv4/af_inet.c:338
Read of size 4 at addr ffff8801bde28554 by task kworker/u4:5/3492

CPU: 0 PID: 3492 Comm: kworker/u4:5 Not tainted 4.15.0-rc2-mm1+ #39
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: krdsd rds_connect_worker
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_load4_noabort+0x14/0x20 mm/kasan/report.c:429
  inet_create+0xda0/0xf50 net/ipv4/af_inet.c:338
  __sock_create+0x4d4/0x850 net/socket.c:1265
  sock_create_kern+0x3f/0x50 net/socket.c:1311
  rds_tcp_conn_path_connect+0x26f/0x920 net/rds/tcp_connect.c:108
  rds_connect_worker+0x156/0x1f0 net/rds/threads.c:165
  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
  kthread+0x37a/0x440 kernel/kthread.c:238
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524

Allocated by task 3362:
  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:3548
  kmem_cache_zalloc include/linux/slab.h:695 [inline]
  net_alloc net/core/net_namespace.c:362 [inline]
  copy_net_ns+0x196/0x580 net/core/net_namespace.c:402
  create_new_namespaces+0x425/0x880 kernel/nsproxy.c:107
  unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:206
  SYSC_unshare kernel/fork.c:2421 [inline]
  SyS_unshare+0x653/0xfa0 kernel/fork.c:2371
  entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 35:
  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:3492 [inline]
  kmem_cache_free+0x77/0x280 mm/slab.c:3750
  net_free+0xca/0x110 net/core/net_namespace.c:378
  net_drop_ns.part.11+0x26/0x30 net/core/net_namespace.c:385
  net_drop_ns net/core/net_namespace.c:384 [inline]
  cleanup_net+0x895/0xb60 net/core/net_namespace.c:502
  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
  kthread+0x37a/0x440 kernel/kthread.c:238
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524

The buggy address belongs to the object at ffff8801bde28080
  which belongs to the cache net_namespace of size 6272
The buggy address is located 1236 bytes inside of
  6272-byte region [ffff8801bde28080, ffff8801bde29900)
The buggy address belongs to the page:
page:00000000df6a4dc0 count:1 mapcount:0 mapping:00000000553659f1 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bde28080 0000000000000000 0000000100000001
raw: ffffea0006f75da0 ffffea0006f60220 ffff8801d989fe00 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801bde28400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801bde28480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801bde28500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                  ^
  ffff8801bde28580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801bde28600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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