netdev - [PATCH net] pkt_sched: fq: do not accept silly TCA_FQ

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Message-Id: <20200106141039.204089-1-edumazet@google.com>
Date:   Mon,  6 Jan 2020 06:10:39 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Florian Westphal <fw@...len.de>,
        syzbot+dc9071cc5a85950bdfce@...kaller.appspotmail.com
Subject: [PATCH net] pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM

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
---
 net/sched/sch_fq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index ff4c5e9d0d7778d86f20f4bd67cc627eed0713d9..a5a295477eccd52952e26e2ce121315341dddd0f 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -786,10 +786,12 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt,
 	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])
-- 
2.24.1.735.g03f4e72817-goog