[PATCH 4.19 016/116] net_sched: cls_route: remove the right filter from hashtable

[Greg Kroah-Hartman]

From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

[ Upstream commit ef299cc3fa1a9e1288665a9fdc8bff55629fd359 ]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-and-tested-by: syzbot+2f8c233f131943d6056d@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 1109c00547fc ("net: sched: RCU cls_route")
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/sched/cls_route.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -536,8 +536,8 @@ static int route4_change(struct net *net
 			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;
 				}
 			}