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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.9 08/90] sch_sfq: validate silly quantum values
Date:   Mon, 18 May 2020 19:35:46 +0200
Message-Id: <20200518173452.906332765@linuxfoundation.org>
In-Reply-To: <20200518173450.930655662@linuxfoundation.org>
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From: Eric Dumazet <edumazet@google.com>

[ Upstream commit df4953e4e997e273501339f607b77953772e3559 ]

syzbot managed to set up sfq so that q->scaled_quantum was zero,
triggering an infinite loop in sfq_dequeue()

More generally, we must only accept quantum between 1 and 2^18 - 7,
meaning scaled_quantum must be in [1, 0x7FFF] range.

Otherwise, we also could have a loop in sfq_dequeue()
if scaled_quantum happens to be 0x8000, since slot->allot
could indefinitely switch between 0 and 0x8000.

Fixes: eeaeb068f139 ("sch_sfq: allow big packets and be fair")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/sched/sch_sfq.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -635,6 +635,15 @@ static int sfq_change(struct Qdisc *sch,
 	if (ctl->divisor &&
 	    (!is_power_of_2(ctl->divisor) || ctl->divisor > 65536))
 		return -EINVAL;
+
+	/* slot->allot is a short, make sure quantum is not too big. */
+	if (ctl->quantum) {
+		unsigned int scaled = SFQ_ALLOT_SIZE(ctl->quantum);
+
+		if (scaled <= 0 || scaled > SHRT_MAX)
+			return -EINVAL;
+	}
+
 	if (ctl_v1 && !red_check_params(ctl_v1->qth_min, ctl_v1->qth_max,
 					ctl_v1->Wlog))
 		return -EINVAL;