net_sched: fix backward compatibility for TCA_ACT_KIND

For TCA_ACT_KIND, we have to keep the backward compatibility too,
and rely on nla_strlcpy() to check and terminate the string with
a NUL.

Note for TC actions, nla_strcmp() is already used to compare kind
strings, so we don't need to fix other places.

Fixes: 199ce850 ("net_sched: add policy validation for action attributes")
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/act_api.c

@@ -832,8 +832,7 @@ static struct tc_cookie *nla_memdup_cookie(struct nlattr **tb)
 }
 
 static const struct nla_policy tcf_action_policy[TCA_ACT_MAX + 1] = {
-	[TCA_ACT_KIND]		= { .type = NLA_NUL_STRING,
-				    .len = IFNAMSIZ - 1 },
+	[TCA_ACT_KIND]		= { .type = NLA_STRING },
 	[TCA_ACT_INDEX]		= { .type = NLA_U32 },
 	[TCA_ACT_COOKIE]	= { .type = NLA_BINARY,
 				    .len = TC_COOKIE_MAX_SIZE },
@@ -865,8 +864,10 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 			NL_SET_ERR_MSG(extack, "TC action kind must be specified");
 			goto err_out;
 		}
-		nla_strlcpy(act_name, kind, IFNAMSIZ);
-
+		if (nla_strlcpy(act_name, kind, IFNAMSIZ) >= IFNAMSIZ) {
+			NL_SET_ERR_MSG(extack, "TC action name too long");
+			goto err_out;
+		}
 		if (tb[TCA_ACT_COOKIE]) {
 			cookie = nla_memdup_cookie(tb);
 			if (!cookie) {