Re: KASAN: use-after-free Write in xfrm_hash_rebuild

[syzbot <syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following crash on:

HEAD commit:    249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f017c3a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
dashboard link: https://syzkaller.appspot.com/bug?extid=0165480d4ef07360eeda
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16cf37c3a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __write_once_size  
include/linux/compiler.h:221 [inline]
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:748 [inline]
BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:455  
[inline]
BUG: KASAN: use-after-free in xfrm_hash_rebuild+0xa0d/0x1000  
net/xfrm/xfrm_policy.c:1318
Write of size 8 at addr ffff888095e79c00 by task kworker/1:3/8066

CPU: 1 PID: 8066 Comm: kworker/1:3 Not tainted 5.2.0-rc6+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events xfrm_hash_rebuild
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
  print_address_description+0x6d/0x310 mm/kasan/report.c:188
  __kasan_report+0x14b/0x1c0 mm/kasan/report.c:317
  kasan_report+0x26/0x50 mm/kasan/common.c:614
  __asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137
  __write_once_size include/linux/compiler.h:221 [inline]
  __hlist_del include/linux/list.h:748 [inline]
  hlist_del_rcu include/linux/rculist.h:455 [inline]
  xfrm_hash_rebuild+0xa0d/0x1000 net/xfrm/xfrm_policy.c:1318
  process_one_work+0x814/0x1130 kernel/workqueue.c:2269
  worker_thread+0xc01/0x1640 kernel/workqueue.c:2415
  kthread+0x325/0x350 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 8064:
  save_stack mm/kasan/common.c:71 [inline]
  set_track mm/kasan/common.c:79 [inline]
  __kasan_kmalloc+0x11c/0x1b0 mm/kasan/common.c:489
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
  __do_kmalloc mm/slab.c:3660 [inline]
  __kmalloc+0x23c/0x310 mm/slab.c:3669
  kmalloc include/linux/slab.h:552 [inline]
  kzalloc include/linux/slab.h:742 [inline]
  xfrm_hash_alloc+0x38/0xe0 net/xfrm/xfrm_hash.c:21
  xfrm_policy_init net/xfrm/xfrm_policy.c:4036 [inline]
  xfrm_net_init+0x269/0xd60 net/xfrm/xfrm_policy.c:4120
  ops_init+0x336/0x420 net/core/net_namespace.c:130
  setup_net+0x212/0x690 net/core/net_namespace.c:316
  copy_net_ns+0x224/0x380 net/core/net_namespace.c:439
  create_new_namespaces+0x4ec/0x700 kernel/nsproxy.c:103
  unshare_nsproxy_namespaces+0x12a/0x190 kernel/nsproxy.c:202
  ksys_unshare+0x540/0xac0 kernel/fork.c:2692
  __do_sys_unshare kernel/fork.c:2760 [inline]
  __se_sys_unshare kernel/fork.c:2758 [inline]
  __x64_sys_unshare+0x38/0x40 kernel/fork.c:2758
  do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 17:
  save_stack mm/kasan/common.c:71 [inline]
  set_track mm/kasan/common.c:79 [inline]
  __kasan_slab_free+0x12a/0x1e0 mm/kasan/common.c:451
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
  __cache_free mm/slab.c:3432 [inline]
  kfree+0xae/0x120 mm/slab.c:3755
  xfrm_hash_free+0x38/0xd0 net/xfrm/xfrm_hash.c:35
  xfrm_bydst_resize net/xfrm/xfrm_policy.c:602 [inline]
  xfrm_hash_resize+0x13f1/0x1840 net/xfrm/xfrm_policy.c:680
  process_one_work+0x814/0x1130 kernel/workqueue.c:2269
  worker_thread+0xc01/0x1640 kernel/workqueue.c:2415
  kthread+0x325/0x350 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the object at ffff888095e79c00
  which belongs to the cache kmalloc-64 of size 64
The buggy address is located 0 bytes inside of
  64-byte region [ffff888095e79c00, ffff888095e79c40)
The buggy address belongs to the page:
page:ffffea0002579e40 refcount:1 mapcount:0 mapping:ffff8880aa400340  
index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002540888 ffffea0002907548 ffff8880aa400340
raw: 0000000000000000 ffff888095e79000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff888095e79b00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
  ffff888095e79b80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffff888095e79c00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                    ^
  ffff888095e79c80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
  ffff888095e79d00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================