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

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

[Davide Caratti]

commit 7041101ff6c3073fd8f2e99920f535b111c929cb upstream.

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.

This patch doesn't use netlink validation helpers, since they might not be
available on all stable branches.

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")
Cc: <stable@vger.kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
---
 net/sched/sch_fq.c | 12 ++++++++++--
 1 file changed, 10 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",
-- 
2.39.2