net/sched: sch_fq: fix integer overflow of "credit"

if sch_fq is configured with "initial quantum" having values greater than
INT_MAX, the first assignment of "credit" does signed integer overflow to
a very negative value.
In this situation, the syzkaller script provided by Cristoph triggers the
CPU soft-lockup warning even with few sockets. It's not an infinite loop,
but "credit" wasn't probably meant to be minus 2Gb for each new flow.
Capping "initial quantum" to INT_MAX proved to fix the issue.

v2: validation of "initial quantum" is done in fq_policy, instead of open
    coding in fq_change() _ suggested by Jakub Kicinski

Reported-by: Christoph Paasch <cpaasch@apple.com>
Link: https://github.com/multipath-tcp/mptcp_net-next/issues/377
Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Link: https://lore.kernel.org/r/7b3a3c7e36d03068707a021760a194a8eb5ad41a.1682002300.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 48d14fb..f59a2cb 100644 (file)
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -779,13 +779,17 @@ static int fq_resize(struct Qdisc *sch, u32 log)
        return 0;
 }
 
+static struct netlink_range_validation iq_range = {
+       .max = INT_MAX,
+};
+
 static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
        [TCA_FQ_UNSPEC]                 = { .strict_start_type = TCA_FQ_TIMER_SLACK },
 
        [TCA_FQ_PLIMIT]                 = { .type = NLA_U32 },
        [TCA_FQ_FLOW_PLIMIT]            = { .type = NLA_U32 },
        [TCA_FQ_QUANTUM]                = { .type = NLA_U32 },
-       [TCA_FQ_INITIAL_QUANTUM]        = { .type = NLA_U32 },
+       [TCA_FQ_INITIAL_QUANTUM]        = NLA_POLICY_FULL_RANGE(NLA_U32, &iq_range),
        [TCA_FQ_RATE_ENABLE]            = { .type = NLA_U32 },
        [TCA_FQ_FLOW_DEFAULT_RATE]      = { .type = NLA_U32 },
        [TCA_FQ_FLOW_MAX_RATE]          = { .type = NLA_U32 },

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json
index 8acb904..3593fb8 100644 (file)
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json
@@ -115,6 +115,28 @@
         ]
     },
     {
+        "id": "10f7",
+        "name": "Create FQ with invalid initial_quantum setting",
+        "category": [
+            "qdisc",
+            "fq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link add dev $DUMMY type dummy || /bin/true"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root fq initial_quantum 0x80000000",
+        "expExitCode": "2",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc fq 1: root.*initial_quantum 2048Mb",
+        "matchCount": "0",
+        "teardown": [
+            "$IP link del dev $DUMMY type dummy"
+        ]
+    },
+    {
         "id": "9398",
         "name": "Create FQ with maxrate setting",
         "category": [