From 50317fce2cc70a2bbbc4b42c31bbad510382a53c Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Fri, 27 Oct 2017 22:08:56 -0700 Subject: [PATCH] net_sched: avoid matching qdisc with zero handle Davide found the following script triggers a NULL pointer dereference: ip l a name eth0 type dummy tc q a dev eth0 parent :1 handle 1: htb This is because for a freshly created netdevice noop_qdisc is attached and when passing 'parent :1', kernel actually tries to match the major handle which is 0 and noop_qdisc has handle 0 so is matched by mistake. Commit 69012ae425d7 tries to fix a similar bug but still misses this case. Handle 0 is not a valid one, should be just skipped. In fact, kernel uses it as TC_H_UNSPEC. Fixes: 69012ae425d7 ("net: sched: fix handling of singleton qdiscs with qdisc_hash") Fixes: 59cc1f61f09c ("net: sched:convert qdisc linked list to hashtable") Reported-by: Davide Caratti Cc: Jiri Kosina Cc: Eric Dumazet Cc: Jamal Hadi Salim Signed-off-by: Cong Wang Signed-off-by: David S. Miller --- net/sched/sch_api.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index c6deb74e3d2f..22bc6fc48311 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -301,6 +301,8 @@ struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle) { struct Qdisc *q; + if (!handle) + return NULL; q = qdisc_match_from_root(dev->qdisc, handle); if (q) goto out; -- 2.30.2