Subject: [PATCH 10/30] net: sched: Fix one possible panic when no destroy callback

From: Gao Feng <[email-masked]>
Date: Wed, 28 Jun 2017 12:53:54 +0800

[ Upstream commit c1a4872ebfb83b1af7144f7b29ac8c4b344a12a8 ]

When qdisc fail to init, qdisc_create would invoke the destroy callback
to cleanup. But there is no check if the callback exists really. So it
would cause the panic if there is no real destroy callback like the qdisc
codel, fq, and so on.

Take codel as an example following:
When a malicious user constructs one invalid netlink msg, it would cause
codel_init->codel_change->nla_parse_nested failed.
Then kernel would invoke the destroy callback directly but qdisc codel
doesn't define one. It causes one panic as a result.

Now add one the check for destroy to avoid the possible panic.

Fixes: 87b60cfacf9f ("net_sched: fix error recovery at qdisc creation")
Signed-off-by: Gao Feng <[email-masked]>
Acked-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/sched/sch_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index bcf49cd22786..6ca1db73d1d1 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1008,7 +1008,8 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 		return sch;
 	}
 	/* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
-	ops->destroy(sch);
+	if (ops->destroy)
+		ops->destroy(sch);
 err_out3:
 	dev_put(dev);
 	kfree((char *) sch - sch->padded);
-- 
2.13.0