linux-kernel - [PATCH 4.19 72/84] pkt_sched: fq: do not accept silly TCA_FQ

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Date:   Sat, 11 Jan 2020 10:50:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        syzbot+dc9071cc5a85950bdfce@...kaller.appspotmail.com,
        "David S. Miller" <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>
Subject: [PATCH 4.19 72/84] pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit d9e15a2733067c9328fb56d98fe8e574fa19ec31 ]

As diagnosed by Florian :

If TCA_FQ_QUANTUM is set to 0x80000000, fq_deueue()
can loop forever in :

if (f->credit <= 0) {
  f->credit += q->quantum;
  goto begin;
}

... because f->credit is either 0 or -2147483648.

Let's limit TCA_FQ_QUANTUM to no more than 1 << 20 :
This max value should limit risks of breaking user setups
while fixing this bug.

Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Diagnosed-by: Florian Westphal <fw@...len.de>
Reported-by: syzbot+dc9071cc5a85950bdfce@...kaller.appspotmail.com
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/sch_fq.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -735,10 +735,12 @@ static int fq_change(struct Qdisc *sch,
 	if (tb[TCA_FQ_QUANTUM]) {
 		u32 quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);
 
-		if (quantum > 0)
+		if (quantum > 0 && quantum <= (1 << 20)) {
 			q->quantum = quantum;
-		else
+		} else {
+			NL_SET_ERR_MSG_MOD(extack, "invalid quantum");
 			err = -EINVAL;
+		}
 	}
 
 	if (tb[TCA_FQ_INITIAL_QUANTUM])