[PATCH v4 net-next 3/9] net/sched: mqprio: add extack to mqprio_parse_nlattr()

[Vladimir Oltean]

Netlink attribute parsing in mqprio is a minesweeper game, with many
options having the possibility of being passed incorrectly and the user
being none the wiser.

Try to make errors less sour by giving user space some information
regarding what went wrong.

Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Reviewed-by: Ferenc Fejes <fejes@xxxxxxxxxxx>
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
---
v1->v4: none

 net/sched/sch_mqprio.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index 94093971da5e..5a9261c38b95 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -150,7 +150,8 @@ static const struct nla_policy mqprio_policy[TCA_MQPRIO_MAX + 1] = {
  * TCA_OPTIONS, which are appended right after struct tc_mqprio_qopt.
  */
 static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
-			       struct nlattr *opt)
+			       struct nlattr *opt,
+			       struct netlink_ext_ack *extack)
 {
 	struct nlattr *nlattr_opt = nla_data(opt) + NLA_ALIGN(sizeof(*qopt));
 	int nlattr_opt_len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
@@ -167,8 +168,11 @@ static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
 			return err;
 	}
 
-	if (!qopt->hw)
+	if (!qopt->hw) {
+		NL_SET_ERR_MSG(extack,
+			       "mqprio TCA_OPTIONS can only contain netlink attributes in hardware mode");
 		return -EINVAL;
+	}
 
 	if (tb[TCA_MQPRIO_MODE]) {
 		priv->flags |= TC_MQPRIO_F_MODE;
@@ -181,13 +185,19 @@ static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
 	}
 
 	if (tb[TCA_MQPRIO_MIN_RATE64]) {
-		if (priv->shaper != TC_MQPRIO_SHAPER_BW_RATE)
+		if (priv->shaper != TC_MQPRIO_SHAPER_BW_RATE) {
+			NL_SET_ERR_MSG_ATTR(extack, tb[TCA_MQPRIO_MIN_RATE64],
+					    "min_rate accepted only when shaper is in bw_rlimit mode");
 			return -EINVAL;
+		}
 		i = 0;
 		nla_for_each_nested(attr, tb[TCA_MQPRIO_MIN_RATE64],
 				    rem) {
-			if (nla_type(attr) != TCA_MQPRIO_MIN_RATE64)
+			if (nla_type(attr) != TCA_MQPRIO_MIN_RATE64) {
+				NL_SET_ERR_MSG_ATTR(extack, attr,
+						    "Attribute type expected to be TCA_MQPRIO_MIN_RATE64");
 				return -EINVAL;
+			}
 			if (i >= qopt->num_tc)
 				break;
 			priv->min_rate[i] = *(u64 *)nla_data(attr);
@@ -197,13 +207,19 @@ static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
 	}
 
 	if (tb[TCA_MQPRIO_MAX_RATE64]) {
-		if (priv->shaper != TC_MQPRIO_SHAPER_BW_RATE)
+		if (priv->shaper != TC_MQPRIO_SHAPER_BW_RATE) {
+			NL_SET_ERR_MSG_ATTR(extack, tb[TCA_MQPRIO_MAX_RATE64],
+					    "max_rate accepted only when shaper is in bw_rlimit mode");
 			return -EINVAL;
+		}
 		i = 0;
 		nla_for_each_nested(attr, tb[TCA_MQPRIO_MAX_RATE64],
 				    rem) {
-			if (nla_type(attr) != TCA_MQPRIO_MAX_RATE64)
+			if (nla_type(attr) != TCA_MQPRIO_MAX_RATE64) {
+				NL_SET_ERR_MSG_ATTR(extack, attr,
+						    "Attribute type expected to be TCA_MQPRIO_MAX_RATE64");
 				return -EINVAL;
+			}
 			if (i >= qopt->num_tc)
 				break;
 			priv->max_rate[i] = *(u64 *)nla_data(attr);
@@ -252,7 +268,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt,
 
 	len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
 	if (len > 0) {
-		err = mqprio_parse_nlattr(sch, qopt, opt);
+		err = mqprio_parse_nlattr(sch, qopt, opt, extack);
 		if (err)
 			return err;
 	}
-- 
2.34.1