netdev - [PATCH net] net/sched: sch_fq: fix integer overflow of "credit"

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Date:   Mon, 17 Apr 2023 13:02:40 +0200
From:   Davide Caratti <dcaratti@...hat.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Christoph Paasch <cpaasch@...le.com>, netdev@...r.kernel.org
Subject: [PATCH net] 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.

Reported-by: Christoph Paasch <cpaasch@...le.com>
Link: https://github.com/multipath-tcp/mptcp_net-next/issues/377
Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/sched/sch_fq.c                            | 12 ++++++++--
 .../tc-testing/tc-tests/qdiscs/fq.json        | 22 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 48d14fb90ba0..12efbcfc2938 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -842,8 +842,16 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt,
 		}
 	}
 
-	if (tb[TCA_FQ_INITIAL_QUANTUM])
-		q->initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]);
+	if (tb[TCA_FQ_INITIAL_QUANTUM]) {
+		u32 initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]);
+
+		if (initial_quantum <= INT_MAX) {
+			q->initial_quantum = initial_quantum;
+		} else {
+			NL_SET_ERR_MSG_MOD(extack, "invalid initial quantum");
+			err = -EINVAL;
+		}
+	}
 
 	if (tb[TCA_FQ_FLOW_DEFAULT_RATE])
 		pr_warn_ratelimited("sch_fq: defrate %u ignored.\n",
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 8acb904d1419..3593fb8f79ad 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/fq.json
@@ -114,6 +114,28 @@
             "$IP link del dev $DUMMY type dummy"
         ]
     },
+    {
+        "id": "10f7",
+        "name": "Create FQ with invalid initial_quantum setting",
+        "category": [
+            "qdisc",
+            "fq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$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",
-- 
2.39.2