Commit 6d4c4077 authored Oct 07, 2018 by Al Viro Committed by David S. Miller Oct 07, 2018

net: sched: cls_u32: fix hnode refcounting



cls_u32.c misuses refcounts for struct tc_u_hnode - it counts references
via ->hlist and via ->tp_root together.  u32_destroy() drops the former
and, in case when there had been links, leaves the sucker on the list.
As the result, there's nothing to protect it from getting freed once links
are dropped.
That also makes the "is it busy" check incapable of catching the root
hnode - it *is* busy (there's a reference from tp), but we don't see it as
something separate.  "Is it our root?" check partially covers that, but
the problem exists for others' roots as well.

AFAICS, the minimal fix preserving the existing behaviour (where it doesn't
include oopsen, that is) would be this:
        * count tp->root and tp_c->hlist as separate references.  I.e.
have u32_init() set refcount to 2, not 1.
	* in u32_destroy() we always drop the former;
in u32_destroy_hnode() - the latter.

	That way we have *all* references contributing to refcount.  List
removal happens in u32_destroy_hnode() (called only when ->refcnt is 1)
an in u32_destroy() in case of tc_u_common going away, along with
everything reachable from it.  IOW, that way we know that
u32_destroy_key() won't free something still on the list (or pointed to by
someone's ->root).

Reproducer:

tc qdisc add dev eth0 ingress
tc filter add dev eth0 parent ffff: protocol ip prio 100 handle 1: \
u32 divisor 1
tc filter add dev eth0 parent ffff: protocol ip prio 200 handle 2: \
u32 divisor 1
tc filter add dev eth0 parent ffff: protocol ip prio 100 \
handle 1:0:11 u32 ht 1: link 801: offset at 0 mask 0f00 shift 6 \
plus 0 eat match ip protocol 6 ff
tc filter delete dev eth0 parent ffff: protocol ip prio 200
tc filter change dev eth0 parent ffff: protocol ip prio 100 \
handle 1:0:11 u32 ht 1: link 0: offset at 0 mask 0f00 shift 6 plus 0 \
eat match ip protocol 6 ff
tc filter delete dev eth0 parent ffff: protocol ip prio 100

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 7e823644

net/sched/cls_u32.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -398,6 +398,7 @@ static int u32_init(struct tcf_proto *tp)
		rcu_assign_pointer(tp_c->hlist, root_ht);
		root_ht->tp_c = tp_c;

		root_ht->refcnt++;
		rcu_assign_pointer(tp->root, root_ht);
		tp->data = tp_c;
		return 0;
		@@ -610,7 +611,7 @@ static int u32_destroy_hnode(struct tcf_proto tp, struct tc_u_hnode ht,
		struct tc_u_hnode __rcu **hn;
		struct tc_u_hnode *phn;

		WARN_ON(ht->refcnt);
		WARN_ON(--ht->refcnt);

		u32_clear_hnode(tp, ht, extack);

		@@ -649,7 +650,7 @@ static void u32_destroy(struct tcf_proto tp, struct netlink_ext_ack extack)

		WARN_ON(root_ht == NULL);

		if (root_ht && --root_ht->refcnt == 0)
		if (root_ht && --root_ht->refcnt == 1)
		u32_destroy_hnode(tp, root_ht, extack);

		if (--tp_c->refcnt == 0) {
		@@ -698,7 +699,6 @@ static int u32_delete(struct tcf_proto tp, void arg, bool *last,
		}

		if (ht->refcnt == 1) {
		ht->refcnt--;
		u32_destroy_hnode(tp, ht, extack);
		} else {
		NL_SET_ERR_MSG_MOD(extack, "Can not delete in-use filter");
		@@ -708,11 +708,11 @@ static int u32_delete(struct tcf_proto tp, void arg, bool *last,
		out:
		*last = true;
		if (root_ht) {
		if (root_ht->refcnt > 1) {
		if (root_ht->refcnt > 2) {
		*last = false;
		goto ret;
		}
		if (root_ht->refcnt == 1) {
		if (root_ht->refcnt == 2) {
		if (!ht_empty(root_ht)) {
		*last = false;
		goto ret;

Admin message