netfilter: conntrack: fix using __this_cpu_add in preemptible

In the Linux kernel, the following vulnerability has been resolved:

netfilter: conntrack: fix using __this_cpu_add in preemptible

Currently in nf_conntrack_hash_check_insert(), when it fails in

nf_ct_ext_valid_pre/post(), NF_CT_STAT_INC() will be called in the

preemptible context, a call trace can be triggered:

BUG: using __this_cpu_add() in preemptible [00000000] code: conntrack/1636

caller is nf_conntrack_hash_check_insert+0x45/0x430 [nf_conntrack]

Call Trace:

<TASK>

dump_stack_lvl+0x33/0x46

check_preemption_disabled+0xc3/0xf0

nf_conntrack_hash_check_insert+0x45/0x430 [nf_conntrack]

ctnetlink_create_conntrack+0x3cd/0x4e0 [nf_conntrack_netlink]

ctnetlink_new_conntrack+0x1c0/0x450 [nf_conntrack_netlink]

nfnetlink_rcv_msg+0x277/0x2f0 [nfnetlink]

netlink_rcv_skb+0x50/0x100

nfnetlink_rcv+0x65/0x144 [nfnetlink]

netlink_unicast+0x1ae/0x290

netlink_sendmsg+0x257/0x4f0

sock_sendmsg+0x5f/0x70

This patch is to fix it by changing to use NF_CT_STAT_INC_ATOMIC() for

nf_ct_ext_valid_pre/post() check in nf_conntrack_hash_check_insert(),

as well as nf_ct_ext_valid_post() in __nf_conntrack_confirm().

Note that nf_ct_ext_valid_pre() check in __nf_conntrack_confirm() is

safe to use NF_CT_STAT_INC(), as it's under local_bh_disable().