This is a note to let you know that I've just added the patch titled net_sched: check error pointer in tcf_dump_walker() to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net_sched-check-error-pointer-in-tcf_dump_walker.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 29fab1449162184edd9029e4a1efc1f59f66b446 Author: Cong Wang <xiyou.wangcong@xxxxxxxxx> Date: Fri Oct 2 12:13:34 2020 -0700 net_sched: check error pointer in tcf_dump_walker() [ Upstream commit 580e4273d7a883ececfefa692c1f96bdbacb99b5 ] Although we take RTNL on dump path, it is possible to skip RTNL on insertion path. So the following race condition is possible: rtnl_lock() // no rtnl lock mutex_lock(&idrinfo->lock); // insert ERR_PTR(-EBUSY) mutex_unlock(&idrinfo->lock); tc_dump_action() rtnl_unlock() So we have to skip those temporary -EBUSY entries on dump path too. Reported-and-tested-by: syzbot+b47bc4f247856fb4d9e1@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 0fedc63fadf0 ("net_sched: commit action insertions together") Cc: Vlad Buslov <vladbu@xxxxxxxxxxxx> Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> Cc: Jiri Pirko <jiri@xxxxxxxxxxx> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/sched/act_api.c b/net/sched/act_api.c index 17e5cd9ebd89..75132d0ca887 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -231,6 +231,8 @@ static int tcf_dump_walker(struct tcf_idrinfo *idrinfo, struct sk_buff *skb, index++; if (index < s_i) continue; + if (IS_ERR(p)) + continue; if (jiffy_since && time_after(jiffy_since,