Describe CVE-2021-47106.
What is CVE-2021-47106?
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: fix use-after-free in nft_set_catchall_destroy()

We need to use list_for_each_entry_safe() iterator
because we can not access @catchall after kfree_rcu() call.

syzbot reported:

BUG: KASAN: use-after-free in nft_set_catchall_destroy net/netfilter/nf_tables_api.c:4486 [inline]
BUG: KASAN: use-after-free in nft_set_destroy net/netfilter/nf_tables_api.c:4504 [inline]
BUG: KASAN: use-after-free in nft_set_destroy+0x3fd/0x4f0 net/netfilter/nf_tables_api.c:4493
Read of size 8 at addr ffff8880716e5b80 by task syz-executor.3/8871

CPU: 1 PID: 8871 Comm: syz-executor.3 Not tainted 5.16.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description.constprop.0.cold+0x8d/0x2ed mm/kasan/report.c:247
 __kasan_report mm/kasan/report.c:433 [inline]
 kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
 nft_set_catchall_destroy net/netfilter/nf_tables_api.c:4486 [inline]
 nft_set_destroy net/netfilter/nf_tables_api.c:4504 [inline]
 nft_set_destroy+0x3fd/0x4f0 net/netfilter/nf_tables_api.c:4493
 __nft_release_table+0x79f/0xcd0 net/netfilter/nf_tables_api.c:9626
 nft_rcv_nl_event+0x4f8/0x670 net/netfilter/nf_tables_api.c:9688
 notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
 blocking_notifier_call_chain kernel/notifier.c:318 [inline]
 blocking_notifier_call_chain+0x67/0x90 kernel/notifier.c:306
 netlink_release+0xcb6/0x1dd0 net/netlink/af_netlink.c:788
 __sock_release+0xcd/0x280 net/socket.c:649
 sock_close+0x18/0x20 net/socket.c:1314
 __fput+0x286/0x9f0 fs/file_table.c:280
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x27e/0x290 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f75fbf28adb
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007ffd8da7ec10 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f75fbf28adb
RDX: 00007f75fc08e828 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007f75fc08a960 R08: 0000000000000000 R09: 00007f75fc08e830
R10: 00007ffd8da7ed10 R11: 0000000000000293 R12: 00000000002067c3
R13: 00007ffd8da7ed10 R14: 00007f75fc088f60 R15: 0000000000000032
 </TASK>

Allocated by task 8886:
 kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 ____kasan_kmalloc mm/kasan/common.c:472 [inline]
 __kasan_kmalloc+0xa6/0xd0 mm/kasan/common.c:522
 kasan_kmalloc include/linux/kasan.h:269 [inline]
 kmem_cache_alloc_trace+0x1ea/0x4a0 mm/slab.c:3575
 kmalloc include/linux/slab.h:590 [inline]
 nft_setelem_catchall_insert net/netfilter/nf_tables_api.c:5544 [inline]
 nft_setelem_insert net/netfilter/nf_tables_api.c:5562 [inline]
 nft_add_set_elem+0x232e/0x2f40 net/netfilter/nf_tables_api.c:5936
 nf_tables_newsetelem+0x6ff/0xbb0 net/netfilter/nf_tables_api.c:6032
 nfnetlink_rcv_batch+0x1710/0x25f0 net/netfilter/nfnetlink.c:513
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:634 [inline]
 nfnetlink_rcv+0x3af/0x420 net/netfilter/nfnetlink.c:652
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x904/0xdf0 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/
---truncated---.