tuntap: fix dividing by zero in ebpf queue selection

mainline inclusion
from mainline-5.1
commit a35d310f03a692bf4798eb309a1950a06a150620
category: bugfix
bugzilla: 13267
CVE: NA

-------------------------------------------------

We need check if tun->numqueues is zero (e.g for the persist device)
before trying to use it for modular arithmetic.
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Fixes: 96f84061("tun: add eBPF based queue selection method")
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Reviewed-by: NMao Wenan <maowenan@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/net/tun.c

@@ -599,13 +599,18 @@ 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,