Patch "net_sched: avoid matching qdisc with zero handle" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

net_sched: avoid matching qdisc with zero handle

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net_sched-avoid-matching-qdisc-with-zero-handle.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Cong Wang <[email protected]>
Date: Fri, 27 Oct 2017 22:08:56 -0700
Subject: net_sched: avoid matching qdisc with zero handle

From: Cong Wang <[email protected]>

[ Upstream commit 50317fce2cc70a2bbbc4b42c31bbad510382a53c ]

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.

---
 net/sched/sch_api.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/tun-call-dev_get_valid_name-before-register_netdevice.patch queue-4.13/net_sched-avoid-matching-qdisc-with-zero-handle.patch queue-4.13/tun-allow-positive-return-values-on-dev_get_valid_name-call.patch