[PATCH net v8 6/6] net/sched: netem: check for negative latency and jitter

[Stephen Hemminger <stephen@networkplumber.org>]

Reject requests with negative latency or jitter.
A negative value added to current timestamp (u64) wraps
to an enormous time_to_send, disabling dequeue.
The original UAPI used u32 for these values; the conversion to 64-bit
time values via TCA_NETEM_LATENCY64 and TCA_NETEM_JITTER64
allowed signed values to reach the kernel without validation.

Jitter is already silently clamped by an abs() in netem_change();
that abs() can be removed in a follow-up once this rejection is in
place.

Fixes: 99803171ef04 ("netem: add uapi to express delay and jitter in nanoseconds")
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 net/sched/sch_netem.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 475c14b3dbdb..bc18e1976b6e 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -826,6 +826,16 @@ static int get_dist_table(struct disttable **tbl, const struct nlattr *attr)
 	return 0;
 }
 
+static int validate_time(const struct nlattr *attr, const char *name,
+			 struct netlink_ext_ack *extack)
+{
+	if (nla_get_s64(attr) < 0) {
+		NL_SET_ERR_MSG_ATTR_FMT(extack, attr, "negative %s", name);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 static int validate_slot(const struct nlattr *attr, struct netlink_ext_ack *extack)
 {
 	const struct tc_netem_slot *c = nla_data(attr);
@@ -1068,6 +1078,18 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
 			goto table_free;
 	}
 
+	if (tb[TCA_NETEM_LATENCY64]) {
+		ret = validate_time(tb[TCA_NETEM_LATENCY64], "latency", extack);
+		if (ret)
+			goto table_free;
+	}
+
+	if (tb[TCA_NETEM_JITTER64]) {
+		ret = validate_time(tb[TCA_NETEM_JITTER64], "jitter", extack);
+		if (ret)
+			goto table_free;
+	}
+
 	sch_tree_lock(sch);
 	/* backup q->clg and q->loss_model */
 	old_clg = q->clg;
-- 
2.53.0