batman-adv: Fix double call of dev_queue_xmit

The net_xmit_eval has side effects because it is not making sure that e
isn't evaluated twice.

    #define net_xmit_eval(e)        ((e) == NET_XMIT_CN ? 0 : (e))

The code requested by David Miller [1]

    return net_xmit_eval(dev_queue_xmit(skb));

will get transformed into

    return ((dev_queue_xmit(skb)) == NET_XMIT_CN ? 0 : (dev_queue_xmit(skb)))

dev_queue_xmit will therefore be tried again (with an already consumed skb)
whenever the return code is not NET_XMIT_CN.

[1] https://lkml.kernel.org/r/20170125.225624.965229145391320056.davem@davemloft.net

Fixes: c33705188c49 ("batman-adv: Treat NET_XMIT_CN as transmit successfully")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c
index d9b2889064a60f05122aaf9ea425c64855295ff6..1489ec27daff5548b072e88648f5cca192f74afa 100644 (file)
--- a/net/batman-adv/send.c
+++ b/net/batman-adv/send.c
@@ -77,6 +77,7 @@ int batadv_send_skb_packet(struct sk_buff *skb,
 {
        struct batadv_priv *bat_priv;
        struct ethhdr *ethhdr;
+       int ret;
 
        bat_priv = netdev_priv(hard_iface->soft_iface);
 
@@ -115,7 +116,8 @@ int batadv_send_skb_packet(struct sk_buff *skb,
         * congestion and traffic shaping, it drops and returns NET_XMIT_DROP
         * (which is > 0). This will not be treated as an error.
         */
-       return net_xmit_eval(dev_queue_xmit(skb));
+       ret = dev_queue_xmit(skb);
+       return net_xmit_eval(ret);
 send_skb_err:
        kfree_skb(skb);
        return NET_XMIT_DROP;