net_sched: add max len check for TCA_KIND

The TCA_KIND attribute is of NLA_STRING which does not check
the NUL char. KMSAN reported an uninit-value of TCA_KIND which
is likely caused by the lack of NUL.

Change it to NLA_NUL_STRING and add a max len too.

Fixes: 8b4c3cdd9d ("net: sched: Add policy validation for tc attributes")
Reported-and-tested-by: [email protected]
Cc: Jamal Hadi Salim <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Acked-by: Jiri Pirko <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>

net/sched/sch_api.c

@@ -1390,7 +1390,8 @@ 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_STRING },
+	[TCA_KIND]		= { .type = NLA_NUL_STRING,
+				    .len = IFNAMSIZ - 1 },
 	[TCA_RATE]		= { .type = NLA_BINARY,
 				    .len = sizeof(struct tc_estimator) },
 	[TCA_STAB]		= { .type = NLA_NESTED },