[PATCH 4.13 33/44] net_sched: avoid matching qdisc with zero handle

From: Greg Kroah-Hartman
Date: Thu Nov 16 2017 - 12:56:30 EST

4.13-stable review patch. If anyone has any objections, please let me know.


From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

[ Upstream commit 50317fce2cc70a2bbbc4b42c31bbad510382a53c ]

Davide found the following script triggers a NULL pointer

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 <dcaratti@xxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/sched/sch_api.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -307,6 +307,8 @@ struct Qdisc *qdisc_lookup(struct net_de
struct Qdisc *q;

+ if (!handle)
+ return NULL;
q = qdisc_match_from_root(dev->qdisc, handle);
if (q)
goto out;