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net_sched: avoid matching qdisc with zero handle

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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 69012ae425
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>
This commit is contained in:
Cong Wang 2017-10-27 22:08:56 -07:00 committed by David S. Miller
parent d04adf1b35
commit 50317fce2c
1 changed files with 2 additions and 0 deletions
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2
net/sched/sch_api.c
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@ -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;