[Devel] [PATCH RHEL7 COMMIT] ms/net_sched: cls_route: remove the right filter from hashtable

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.151.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.151.3
------>
commit bbb79af77a24fbb7dbe9ef26b4d536c5a7abfe38
Author: Cong Wang <xiyou.wangcong at gmail.com>
Date:   Fri Mar 13 22:29:54 2020 -0700

    ms/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 at syzkaller.appspotmail.com
    Reported-and-tested-by: syzbot+2f8c233f131943d6056d at syzkaller.appspotmail.com
    Reported-and-tested-by: syzbot+9c2df9fd5e9445b74e01 at syzkaller.appspotmail.com
    Fixes: 1109c00547fc ("net: sched: RCU cls_route")
    Cc: Jamal Hadi Salim <jhs at mojatatu.com>
    Cc: Jiri Pirko <jiri at resnulli.us>
    Cc: John Fastabend <john.fastabend at gmail.com>
    Signed-off-by: Cong Wang <xiyou.wangcong at gmail.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    https://jira.sw.ru/browse/PSBM-104057
    
    (cherry picked from commit ef299cc3fa1a9e1288665a9fdc8bff55629fd359)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.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 7bd464e8d084b..2fed29fa504e4 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;
 				}
 			}