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 <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jamal Hadi Salim <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index c6deb74e3d2f4a007554b9cf78e4ddf7b7b84535..22bc6fc4831116d75027a3871e7854e07b823d71 100644 (file)
--- 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;