[PATCH 4.19 102/113] tuntap: fix dividing by zero in ebpf queue selection

[Greg Kroah-Hartman]

From: Jason Wang <jasow...@redhat.com>

[ Upstream commit a35d310f03a692bf4798eb309a1950a06a150620 ]

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.duma...@gmail.com>
Fixes: 96f84061620c6("tun: add eBPF based queue selection method")
Signed-off-by: Jason Wang <jasow...@redhat.com>
Reviewed-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/tun.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -599,13 +599,18 @@ static u16 tun_automq_select_queue(struc
 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,