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. Commit69012ae425
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:69012ae425
("net: sched: fix handling of singleton qdiscs with qdisc_hash") Fixes:59cc1f61f0
("net: sched:convert qdisc linked list to hashtable") Reported-by: Davide Caratti <dcaratti@redhat.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Eric Dumazet <edumazet@google.com> Cc: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -301,6 +301,8 @@ struct Qdisc *qdisc_lookup(struct net_device *dev, u32 handle)
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{
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{
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struct Qdisc *q;
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struct Qdisc *q;
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if (!handle)
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return NULL;
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q = qdisc_match_from_root(dev->qdisc, handle);
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q = qdisc_match_from_root(dev->qdisc, handle);
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if (q)
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if (q)
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goto out;
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goto out;
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