net/sched: taprio: extend minimum interval restriction to entire cycle too

It is possible for syzbot to side-step the restriction imposed by the
blamed commit in the Fixes: tag, because the taprio UAPI permits a
cycle-time different from (and potentially shorter than) the sum of
entry intervals.

We need one more restriction, which is that the cycle time itself must
be larger than N * ETH_ZLEN bit times, where N is the number of schedule
entries. This restriction needs to apply regardless of whether the cycle
time came from the user or was the implicit, auto-calculated value, so
we move the existing "cycle == 0" check outside the "if "(!new->cycle_time)"
branch. This way covers both conditions and scenarios.

Add a selftest which illustrates the issue triggered by syzbot.

Fixes: b5b73b26b3ca ("taprio: Fix allowing too small intervals")
Reported-by: syzbot+a7d2b1d5d1af83035567@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/0000000000007d66bc06196e7c66@google.com/
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20240527153955.553333-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 11891505536081c2770fefac5fc73779309dd7a1..937a0c513c174b837225c400b4c3ad9915244810 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1151,11 +1151,6 @@ static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb,
                list_for_each_entry(entry, &new->entries, list)
                        cycle = ktime_add_ns(cycle, entry->interval);
 
-               if (!cycle) {
-                       NL_SET_ERR_MSG(extack, "'cycle_time' can never be 0");
-                       return -EINVAL;
-               }
-
                if (cycle < 0 || cycle > INT_MAX) {
                        NL_SET_ERR_MSG(extack, "'cycle_time' is too big");
                        return -EINVAL;
@@ -1164,6 +1159,11 @@ static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb,
                new->cycle_time = cycle;
        }
 
+       if (new->cycle_time < new->num_entries * length_to_duration(q, ETH_ZLEN)) {
+               NL_SET_ERR_MSG(extack, "'cycle_time' is too small");
+               return -EINVAL;
+       }
+
        taprio_calculate_gate_durations(q, new);
 
        return 0;

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
index 8f12f00a4f5720725bafbedcd5e19a5a9f7ee757..557fb074acf0ca4e7a5ee0e31b306f2e3ac3725a 100644 (file)
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
@@ -154,6 +154,28 @@
             "echo \"1\" > /sys/bus/netdevsim/del_device"
         ]
     },
+    {
+        "id": "831f",
+        "name": "Add taprio Qdisc with too short cycle-time",
+        "category": [
+            "qdisc",
+            "taprio"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "echo \"1 1 8\" > /sys/bus/netdevsim/new_device"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $ETH root handle 1: taprio num_tc 2 queues 1@0 1@1 sched-entry S 01 200000 sched-entry S 02 200000 cycle-time 100 clockid CLOCK_TAI",
+        "expExitCode": "2",
+        "verifyCmd": "$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",