net/sched: taprio: make q->picos_per_byte available to fill_sched_entry()

JIRA: https://issues.redhat.com/browse/RHEL-44375
JIRA: https://issues.redhat.com/browse/RHEL-45534
CVE: CVE-2024-36244
Upstream Status: net.git commit e634134

commit e634134
Author: Vladimir Oltean <vladimir.oltean@nxp.com>
Date:   Mon May 27 18:39:54 2024 +0300

    net/sched: taprio: make q->picos_per_byte available to fill_sched_entry()

    In commit b5b73b2 ("taprio: Fix allowing too small intervals"), a
    comparison of user input against length_to_duration(q, ETH_ZLEN) was
    introduced, to avoid RCU stalls due to frequent hrtimers.

    The implementation of length_to_duration() depends on q->picos_per_byte
    being set for the link speed. The blamed commit in the Fixes: tag has
    moved this too late, so the checks introduced above are ineffective.
    The q->picos_per_byte is zero at parse_taprio_schedule() ->
    parse_sched_list() -> parse_sched_entry() -> fill_sched_entry() time.

    Move the taprio_set_picos_per_byte() call as one of the first things in
    taprio_change(), before the bulk of the netlink attribute parsing is
    done. That's because it is needed there.

    Add a selftest to make sure the issue doesn't get reintroduced.

    Fixes: 09dbdf2 ("net/sched: taprio: fix calculation of maximum gate durations")
    Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://lore.kernel.org/r/20240527153955.553333-1-vladimir.oltean@nxp.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

net/sched/sch_taprio.c

@@ -1871,6 +1871,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 
 	q->flags = err;
 
+	/* Needed for length_to_duration() during netlink attribute parsing */
+	taprio_set_picos_per_byte(dev, q);
+
 	err = taprio_parse_mqprio_opt(dev, mqprio, extack, q->flags);
 	if (err < 0)
 		return err;
@@ -1930,7 +1933,6 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 	if (err < 0)
 		goto free_sched;
 
-	taprio_set_picos_per_byte(dev, q);
 	taprio_update_queue_max_sdu(q, new_admin, stab);
 
 	if (FULL_OFFLOAD_IS_ENABLED(q->flags))

tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json

@@ -132,6 +132,28 @@
             "echo \"1\" > /sys/bus/netdevsim/del_device"
         ]
     },
+    {
+        "id": "6f62",
+        "name": "Add taprio Qdisc with too short interval",
+        "category": [
+            "qdisc",
+            "taprio"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "echo \"1 1 8\" > /sys/bus/netdevsim/new_device"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $ETH root handle 1: taprio num_tc 2 queues 1@0 1@1 sched-entry S 01 300 sched-entry S 02 1700 clockid CLOCK_TAI",
+        "expExitCode": "2",
+        "verifyCmd": "$TC qdisc show dev $ETH",
+        "matchPattern": "qdisc taprio 1: root refcnt",
+        "matchCount": "0",
+        "teardown": [
+            "echo \"1\" > /sys/bus/netdevsim/del_device"
+        ]
+    },
     {
         "id": "3e1e",
         "name": "Add taprio Qdisc with an invalid cycle-time",