netdev - [Patch net] net_sched: cls_route: remove the right filter from hashtable

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Message-Id: <20200314052954.26885-1-xiyou.wangcong@gmail.com>
Date:   Fri, 13 Mar 2020 22:29:54 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+f9b32aaacd60305d9687@...kaller.appspotmail.com,
        syzbot+2f8c233f131943d6056d@...kaller.appspotmail.com,
        syzbot+9c2df9fd5e9445b74e01@...kaller.appspotmail.com,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        John Fastabend <john.fastabend@...il.com>
Subject: [Patch net] net_sched: cls_route: remove the right filter from hashtable

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@...kaller.appspotmail.com
Reported-and-tested-by: syzbot+2f8c233f131943d6056d@...kaller.appspotmail.com
Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01@...kaller.appspotmail.com
Fixes: 1109c00547fc ("net: sched: RCU cls_route")
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Cc: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/cls_route.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c
index 6f8786b06bde..5efa3e7ace15 100644
--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -534,8 +534,8 @@ 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;
 				}
 			}
-- 
2.21.1