net_sched: fix backward compatibility for TCA_KIND

Marcelo noticed a backward compatibility issue of TCA_KIND
after we move from NLA_STRING to NLA_NUL_STRING, so it is probably
too late to change it.

Instead, to make everyone happy, we can just insert a NUL to
terminate the string with nla_strlcpy() like we do for TC actions.

Fixes: 62794fc4 ("net_sched: add max len check for TCA_KIND")
Reported-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

net/sched/cls_api.c

@@ -162,11 +162,22 @@ static inline u32 tcf_auto_prio(struct tcf_proto *tp)
 	return TC_H_MAJ(first);
 }
 
+static bool tcf_proto_check_kind(struct nlattr *kind, char *name)
+{
+	if (kind)
+		return nla_strlcpy(name, kind, IFNAMSIZ) >= IFNAMSIZ;
+	memset(name, 0, IFNAMSIZ);
+	return false;
+}
+
 static bool tcf_proto_is_unlocked(const char *kind)
 {
 	const struct tcf_proto_ops *ops;
 	bool ret;
 
+	if (strlen(kind) == 0)
+		return false;
+
 	ops = tcf_proto_lookup_ops(kind, false, NULL);
 	/* On error return false to take rtnl lock. Proto lookup/create
 	 * functions will perform lookup again and properly handle errors.
@@ -1843,6 +1854,7 @@ static int tc_new_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 {
 	struct net *net = sock_net(skb->sk);
 	struct nlattr *tca[TCA_MAX + 1];
+	char name[IFNAMSIZ];
 	struct tcmsg *t;
 	u32 protocol;
 	u32 prio;
@@ -1899,13 +1911,19 @@ static int tc_new_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 	if (err)
 		return err;
 
+	if (tcf_proto_check_kind(tca[TCA_KIND], name)) {
+		NL_SET_ERR_MSG(extack, "Specified TC filter name too long");
+		err = -EINVAL;
+		goto errout;
+	}
+
 	/* Take rtnl mutex if rtnl_held was set to true on previous iteration,
 	 * block is shared (no qdisc found), qdisc is not unlocked, classifier
 	 * type is not specified, classifier is not unlocked.
 	 */
 	if (rtnl_held ||
 	    (q && !(q->ops->cl_ops->flags & QDISC_CLASS_OPS_DOIT_UNLOCKED)) ||
-	    !tca[TCA_KIND] || !tcf_proto_is_unlocked(nla_data(tca[TCA_KIND]))) {
+	    !tcf_proto_is_unlocked(name)) {
 		rtnl_held = true;
 		rtnl_lock();
 	}
@@ -2063,6 +2081,7 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 {
 	struct net *net = sock_net(skb->sk);
 	struct nlattr *tca[TCA_MAX + 1];
+	char name[IFNAMSIZ];
 	struct tcmsg *t;
 	u32 protocol;
 	u32 prio;
@@ -2102,13 +2121,18 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 	if (err)
 		return err;
 
+	if (tcf_proto_check_kind(tca[TCA_KIND], name)) {
+		NL_SET_ERR_MSG(extack, "Specified TC filter name too long");
+		err = -EINVAL;
+		goto errout;
+	}
 	/* Take rtnl mutex if flushing whole chain, block is shared (no qdisc
 	 * found), qdisc is not unlocked, classifier type is not specified,
 	 * classifier is not unlocked.
 	 */
 	if (!prio ||
 	    (q && !(q->ops->cl_ops->flags & QDISC_CLASS_OPS_DOIT_UNLOCKED)) ||
-	    !tca[TCA_KIND] || !tcf_proto_is_unlocked(nla_data(tca[TCA_KIND]))) {
+	    !tcf_proto_is_unlocked(name)) {
 		rtnl_held = true;
 		rtnl_lock();
 	}
@@ -2216,6 +2240,7 @@ static int tc_get_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 {
 	struct net *net = sock_net(skb->sk);
 	struct nlattr *tca[TCA_MAX + 1];
+	char name[IFNAMSIZ];
 	struct tcmsg *t;
 	u32 protocol;
 	u32 prio;
@@ -2252,12 +2277,17 @@ static int tc_get_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 	if (err)
 		return err;
 
+	if (tcf_proto_check_kind(tca[TCA_KIND], name)) {
+		NL_SET_ERR_MSG(extack, "Specified TC filter name too long");
+		err = -EINVAL;
+		goto errout;
+	}
 	/* Take rtnl mutex if block is shared (no qdisc found), qdisc is not
 	 * unlocked, classifier type is not specified, classifier is not
 	 * unlocked.
 	 */
 	if ((q && !(q->ops->cl_ops->flags & QDISC_CLASS_OPS_DOIT_UNLOCKED)) ||
-	    !tca[TCA_KIND] || !tcf_proto_is_unlocked(nla_data(tca[TCA_KIND]))) {
+	    !tcf_proto_is_unlocked(name)) {
 		rtnl_held = true;
 		rtnl_lock();
 	}

net/sched/sch_api.c

@@ -1390,8 +1390,7 @@ check_loop_fn(struct Qdisc *q, unsigned long cl, struct qdisc_walker *w)
 }
 
 const struct nla_policy rtm_tca_policy[TCA_MAX + 1] = {
-	[TCA_KIND]		= { .type = NLA_NUL_STRING,
-				    .len = IFNAMSIZ - 1 },
+	[TCA_KIND]		= { .type = NLA_STRING },
 	[TCA_RATE]		= { .type = NLA_BINARY,
 				    .len = sizeof(struct tc_estimator) },
 	[TCA_STAB]		= { .type = NLA_NESTED },