netfilter: conntrack: re-fetch conntrack after insertion

stable inclusion
from stable-v5.10.120
commit 91a36ec160ec1a0c8f5352b772dffcbb0b6023e3
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BR

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91a36ec160ec1a0c8f5352b772dffcbb0b6023e3



--------------------------------

commit 56b14ece upstream.

In case the conntrack is clashing, insertion can free skb->_nfct and
set skb->_nfct to the already-confirmed entry.

This wasn't found before because the conntrack entry and the extension
space used to free'd after an rcu grace period, plus the race needs
events enabled to trigger.

Reported-by:  <syzbot+793a590957d9c1b96620@syzkaller.appspotmail.com>
Fixes: 71d8c47f ("netfilter: conntrack: introduce clash resolution on insertion race")
Fixes: 2ad9d774 ("netfilter: conntrack: free extension area immediately")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>