KASAN: use-after-free Write in xfrm_hash_rebuild

KASAN: use-after-free Write in xfrm_hash_rebuild

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    601e6bcc Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1534f3d0a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4005028a9d5ddac8
dashboard link: https://syzkaller.appspot.com/bug?extid=0165480d4ef07360eeda
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

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:220 [inline]
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:713 [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+0xfff/0x10f0  
net/xfrm/xfrm_policy.c:1317
Write of size 8 at addr ffff888098529100 by task kworker/0:0/5

CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.1.0+ #4
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+0x172/0x1f0 lib/dump_stack.c:113
  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
  __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
  kasan_report+0x12/0x20 mm/kasan/common.c:614
  __asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137
  __write_once_size include/linux/compiler.h:220 [inline]
  __hlist_del include/linux/list.h:713 [inline]
  hlist_del_rcu include/linux/rculist.h:455 [inline]
  xfrm_hash_rebuild+0xfff/0x10f0 net/xfrm/xfrm_policy.c:1317
  process_one_work+0x98e/0x1790 kernel/workqueue.c:2268
  worker_thread+0x98/0xe40 kernel/workqueue.c:2414
  kthread+0x357/0x430 kernel/kthread.c:253
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

Allocated by task 8152:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_kmalloc mm/kasan/common.c:489 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
  kmem_cache_alloc_node_trace+0x153/0x720 mm/slab.c:3630
  kmalloc_node include/linux/slab.h:585 [inline]
  kzalloc_node include/linux/slab.h:753 [inline]
  __get_vm_area_node+0x12b/0x3a0 mm/vmalloc.c:1401
  __vmalloc_node_range+0xd4/0x790 mm/vmalloc.c:1840
  __vmalloc_node mm/vmalloc.c:1900 [inline]
  __vmalloc_node_flags mm/vmalloc.c:1914 [inline]
  vzalloc+0x6b/0x90 mm/vmalloc.c:1959
  alloc_counters.isra.0+0x53/0x690 net/ipv6/netfilter/ip6_tables.c:819
  copy_entries_to_user net/ipv4/netfilter/arp_tables.c:674 [inline]
  get_entries net/ipv4/netfilter/arp_tables.c:861 [inline]
  do_arpt_get_ctl+0x4a0/0x820 net/ipv4/netfilter/arp_tables.c:1482
  nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
  nf_getsockopt+0x80/0xe0 net/netfilter/nf_sockopt.c:122
  ip_getsockopt net/ipv4/ip_sockglue.c:1574 [inline]
  ip_getsockopt+0x176/0x1d0 net/ipv4/ip_sockglue.c:1554
  tcp_getsockopt net/ipv4/tcp.c:3623 [inline]
  tcp_getsockopt+0x95/0xf0 net/ipv4/tcp.c:3617
  sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:3089
  __sys_getsockopt+0x168/0x250 net/socket.c:2115
  __do_sys_getsockopt net/socket.c:2126 [inline]
  __se_sys_getsockopt net/socket.c:2123 [inline]
  __x64_sys_getsockopt+0xbe/0x150 net/socket.c:2123
  do_syscall_64+0x103/0x670 arch/x86/entry/common.c:298
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8152:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
  __cache_free mm/slab.c:3463 [inline]
  kfree+0xcf/0x230 mm/slab.c:3786
  __vunmap+0x704/0x9c0 mm/vmalloc.c:1617
  __vfree+0x41/0xd0 mm/vmalloc.c:1658
  vfree+0x5f/0x90 mm/vmalloc.c:1688
  copy_entries_to_user net/ipv4/netfilter/arp_tables.c:706 [inline]
  get_entries net/ipv4/netfilter/arp_tables.c:861 [inline]
  do_arpt_get_ctl+0x67b/0x820 net/ipv4/netfilter/arp_tables.c:1482
  nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
  nf_getsockopt+0x80/0xe0 net/netfilter/nf_sockopt.c:122
  ip_getsockopt net/ipv4/ip_sockglue.c:1574 [inline]
  ip_getsockopt+0x176/0x1d0 net/ipv4/ip_sockglue.c:1554
  tcp_getsockopt net/ipv4/tcp.c:3623 [inline]
  tcp_getsockopt+0x95/0xf0 net/ipv4/tcp.c:3617
  sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:3089
  __sys_getsockopt+0x168/0x250 net/socket.c:2115
  __do_sys_getsockopt net/socket.c:2126 [inline]
  __se_sys_getsockopt net/socket.c:2123 [inline]
  __x64_sys_getsockopt+0xbe/0x150 net/socket.c:2123
  do_syscall_64+0x103/0x670 arch/x86/entry/common.c:298
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888098529100
  which belongs to the cache kmalloc-64 of size 64
The buggy address is located 0 bytes inside of
  64-byte region [ffff888098529100, ffff888098529140)
The buggy address belongs to the page:
page:ffffea0002614a40 count:1 mapcount:0 mapping:ffff8880aa400340  
index:0xffff888098529600
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002a22fc8 ffffea00026d2888 ffff8880aa400340
raw: ffff888098529600 ffff888098529000 000000010000001b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff888098529000: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
  ffff888098529080: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffff888098529100: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                    ^
  ffff888098529180: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
  ffff888098529200: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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

[syzbot]

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
==================================================================

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

[syzbot]

syzbot has bisected this bug to:

commit 1548bc4e0512700cf757192c106b3a20ab639223
Author: Florian Westphal <fw@strlen.de>
Date:   Fri Jan 4 13:17:02 2019 +0000

     xfrm: policy: delete inexact policies from inexact list on hash rebuild

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1734cba9a00000
start commit:   249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=14b4cba9a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=10b4cba9a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
dashboard link: https://syzkaller.appspot.com/bug?extid=0165480d4ef07360eeda
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16cf37c3a00000

Reported-by: syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com
Fixes: 1548bc4e0512 ("xfrm: policy: delete inexact policies from inexact  
list on hash rebuild")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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

[Florian Westphal]

syzbot <syzbot+0165480d4ef07360eeda@syzkaller.appspotmail.com> wrote:
> syzbot has bisected this bug to:
> 
> commit 1548bc4e0512700cf757192c106b3a20ab639223
> Author: Florian Westphal <fw@strlen.de>
> Date:   Fri Jan 4 13:17:02 2019 +0000
> 
>     xfrm: policy: delete inexact policies from inexact list on hash rebuild

I'm looking at this now.

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

[Dmitry Vyukov]

On Tue, Jul 2, 2019 at 8:38 AM Hillf Danton <hdanton@sina.com> wrote:
>
>
> On Wed, 26 Jun 2019 20:59:05 -0700 (PDT)
> > 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
> > ==================================================================
> >
>
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -1203,6 +1203,11 @@ xfrm_policy_inexact_insert(struct xfrm_policy *policy, u8 dir, int excl)
>         return delpol;
>  }
>
> +static inline bool xfrm_policy_node_hashed(struct hlist_node *node)
> +{
> +       return node->pprev && node->pprev != LIST_POISON2;

Is it right to open code LIST_POISON2 use here? As far as I see all
current uses of LIST_POISON2 are encapsulated in list functions.

> +}
> +
>  static void xfrm_hash_rebuild(struct work_struct *work)
>  {
>         struct net *net = container_of(work, struct net,
> @@ -1315,7 +1320,9 @@ static void xfrm_hash_rebuild(struct work_struct *work)
>                 chain = policy_hash_bysel(net, &policy->selector,
>                                           policy->family, dir);
>
> -               hlist_del_rcu(&policy->bydst);
> +               /* check bydst still hashed in case that policy survived bydst resize */
> +               if (xfrm_policy_node_hashed(&policy->bydst))
> +                       hlist_del_rcu(&policy->bydst);
>
>                 if (!chain) {
>                         void *p = xfrm_policy_inexact_insert(policy, dir, 0);
> --