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Date:   Wed,  8 May 2019 23:20:17 -0400
From:   Jason Wang <jasowang@...hat.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     yuehaibing@...wei.com, xiyou.wangcong@...il.com,
        weiyongjun1@...wei.com, eric.dumazet@...il.com,
        Jason Wang <jasowang@...hat.com>
Subject: [PATCH net V3 1/2] tuntap: fix dividing by zero in ebpf queue selection

We need check if tun->numqueues is zero (e.g for the persist device)
before trying to use it for modular arithmetic.

Reported-by: Eric Dumazet <eric.dumazet@...il.com>
Fixes: 96f84061620c6("tun: add eBPF based queue selection method")
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/tun.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e9ca1c0..dc62fc3 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -596,13 +596,18 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 {
 	struct tun_prog *prog;
+	u32 numqueues;
 	u16 ret = 0;
 
+	numqueues = READ_ONCE(tun->numqueues);
+	if (!numqueues)
+		return 0;
+
 	prog = rcu_dereference(tun->steering_prog);
 	if (prog)
 		ret = bpf_prog_run_clear_cb(prog->prog, skb);
 
-	return ret % tun->numqueues;
+	return ret % numqueues;
 }
 
 static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
-- 
1.8.3.1

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