taprio: validate TCA_TAPRIO_ATTR_FLAGS through policy instead of open-coding

As of now, the field TCA_TAPRIO_ATTR_FLAGS is being validated by manually
checking its value, using the function taprio_flags_valid().

With this patch, the field will be validated through the netlink policy
NLA_POLICY_MASK, where the mask is defined by TAPRIO_SUPPORTED_FLAGS.
The mutual exclusivity of the two flags TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD
and TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST is still checked manually.

Changes since RFC:
- fixed reversed xmas tree
- use NL_SET_ERR_MSG_MOD() for both invalid configuration

Changes since v1:
- Changed NL_SET_ERR_MSG_MOD to NL_SET_ERR_MSG_ATTR when wrong flags
  issued
- Changed __u32 to u32

Changes since v2:
- Added the missing parameter for NL_SET_ERR_MSG_ATTR (sorry again for
  the noise)
Signed-off-by: Alessandro Marcolini <alessandromarcolini99@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_taprio.c

@@ -40,6 +40,8 @@ static struct static_key_false taprio_have_working_mqprio;
 
 #define TXTIME_ASSIST_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST)
 #define FULL_OFFLOAD_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
+#define TAPRIO_SUPPORTED_FLAGS \
+	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
 #define TAPRIO_FLAGS_INVALID U32_MAX
 
 struct sched_entry {
@@ -408,19 +410,6 @@ static bool is_valid_interval(struct sk_buff *skb, struct Qdisc *sch)
 	return entry;
 }
 
-static bool taprio_flags_valid(u32 flags)
-{
-	/* Make sure no other flag bits are set. */
-	if (flags & ~(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST |
-		      TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD))
-		return false;
-	/* txtime-assist and full offload are mutually exclusive */
-	if ((flags & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST) &&
-	    (flags & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD))
-		return false;
-	return true;
-}
-
 /* This returns the tstamp value set by TCP in terms of the set clock. */
 static ktime_t get_tcp_tstamp(struct taprio_sched *q, struct sk_buff *skb)
 {
@@ -1031,7 +1020,8 @@ static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
 	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]           =
 		NLA_POLICY_FULL_RANGE_SIGNED(NLA_S64, &taprio_cycle_time_range),
 	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION] = { .type = NLA_S64 },
-	[TCA_TAPRIO_ATTR_FLAGS]                      = { .type = NLA_U32 },
+	[TCA_TAPRIO_ATTR_FLAGS]                      =
+		NLA_POLICY_MASK(NLA_U32, TAPRIO_SUPPORTED_FLAGS),
 	[TCA_TAPRIO_ATTR_TXTIME_DELAY]		     = { .type = NLA_U32 },
 	[TCA_TAPRIO_ATTR_TC_ENTRY]		     = { .type = NLA_NESTED },
 };
@@ -1815,33 +1805,6 @@ static int taprio_mqprio_cmp(const struct net_device *dev,
 	return 0;
 }
 
-/* The semantics of the 'flags' argument in relation to 'change()'
- * requests, are interpreted following two rules (which are applied in
- * this order): (1) an omitted 'flags' argument is interpreted as
- * zero; (2) the 'flags' of a "running" taprio instance cannot be
- * changed.
- */
-static int taprio_new_flags(const struct nlattr *attr, u32 old,
-			    struct netlink_ext_ack *extack)
-{
-	u32 new = 0;
-
-	if (attr)
-		new = nla_get_u32(attr);
-
-	if (old != TAPRIO_FLAGS_INVALID && old != new) {
-		NL_SET_ERR_MSG_MOD(extack, "Changing 'flags' of a running schedule is not supported");
-		return -EOPNOTSUPP;
-	}
-
-	if (!taprio_flags_valid(new)) {
-		NL_SET_ERR_MSG_MOD(extack, "Specified 'flags' are not valid");
-		return -EINVAL;
-	}
-
-	return new;
-}
-
 static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 			 struct netlink_ext_ack *extack)
 {
@@ -1852,6 +1815,7 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 	struct net_device *dev = qdisc_dev(sch);
 	struct tc_mqprio_qopt *mqprio = NULL;
 	unsigned long flags;
+	u32 taprio_flags;
 	ktime_t start;
 	int i, err;
 
@@ -1863,12 +1827,28 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 	if (tb[TCA_TAPRIO_ATTR_PRIOMAP])
 		mqprio = nla_data(tb[TCA_TAPRIO_ATTR_PRIOMAP]);
 
-	err = taprio_new_flags(tb[TCA_TAPRIO_ATTR_FLAGS],
-			       q->flags, extack);
-	if (err < 0)
-		return err;
+	/* The semantics of the 'flags' argument in relation to 'change()'
+	 * requests, are interpreted following two rules (which are applied in
+	 * this order): (1) an omitted 'flags' argument is interpreted as
+	 * zero; (2) the 'flags' of a "running" taprio instance cannot be
+	 * changed.
+	 */
+	taprio_flags = tb[TCA_TAPRIO_ATTR_FLAGS] ? nla_get_u32(tb[TCA_TAPRIO_ATTR_FLAGS]) : 0;
 
-	q->flags = err;
+	/* txtime-assist and full offload are mutually exclusive */
+	if ((taprio_flags & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST) &&
+	    (taprio_flags & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[TCA_TAPRIO_ATTR_FLAGS],
+				    "TXTIME_ASSIST and FULL_OFFLOAD are mutually exclusive");
+		return -EINVAL;
+	}
+
+	if (q->flags != TAPRIO_FLAGS_INVALID && q->flags != taprio_flags) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Changing 'flags' of a running schedule is not supported");
+		return -EOPNOTSUPP;
+	}
+	q->flags = taprio_flags;
 
 	err = taprio_parse_mqprio_opt(dev, mqprio, extack, q->flags);
 	if (err < 0)