net_sched: cls_route: remove the right filter from hashtable

stable inclusion
from linux-4.19.114
commit ea3d6652c240978736a91b9e85fde9fee9359be4

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

[ Upstream commit ef299cc3 ]

route4_change() allocates a new filter and copies values from
the old one. After the new filter is inserted into the hash
table, the old filter should be removed and freed, as the final
step of the update.

However, the current code mistakenly removes the new one. This
looks apparently wrong to me, and it causes double "free" and
use-after-free too, as reported by syzbot.

Reported-and-tested-by: syzbot+f9b32aaacd60305d9687@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+2f8c233f131943d6056d@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01@syzkaller.appspotmail.com
Fixes: 1109c005 ("net: sched: RCU cls_route")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NLi Aichun <liaichun@huawei.com>
Reviewed-by: Nguodeqing <geffrey.guo@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/sched/cls_route.c

@@ -536,8 +536,8 @@ static int route4_change(struct net *net, struct sk_buff *in_skb,
 			fp = &b->ht[h];
 			for (pfp = rtnl_dereference(*fp); pfp;
 			     fp = &pfp->next, pfp = rtnl_dereference(*fp)) {
-				if (pfp == f) {
-					*fp = f->next;
+				if (pfp == fold) {
+					rcu_assign_pointer(*fp, fold->next);
 					break;
 				}
 			}