net_sched: cls_route: remove the right filter from hashtable

[ 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@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+2f8c233f131943d6056d@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01@syzkaller.appspotmail.com
Fixes: 1109c00547fc ("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: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c
index ac9a5b8825b9d572a0e60453fc6c68e82bdab320..4f133faa9e60d73808770358877732af3b02d29d 100644 (file)
--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -539,8 +539,8 @@ 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;
                                }
                        }