[PATCH net 6/9] batman-adv: fix TX priority extraction for BATADV_FORW_MCAST

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

batadv_mcast_forw_mode_by_count() pushs the skb->data for BATADV_FORW_MCAST
forwarding via batadv_mcast_forw_mcsend(). But the
batadv_skb_set_priority() expects the ethernet header directly before
(skb->data + offset). With the moved skb->data, just some random data would
be accessed to get the priority data.

Move the batadv_skb_set_priority() before the decision about the handling
multicast packets and potential header modifications.

Cc: stable@vger.kernel.org
Fixes: 90039133221e ("batman-adv: mcast: implement multicast packet generation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/mesh-interface.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/mesh-interface.c b/net/batman-adv/mesh-interface.c
index 8e55b61dd2a64..e202088cf1fd4 100644
--- a/net/batman-adv/mesh-interface.c
+++ b/net/batman-adv/mesh-interface.c
@@ -305,6 +305,8 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 	if (batadv_compare_eth(ethhdr->h_dest, ectp_addr))
 		goto dropped;
 
+	batadv_skb_set_priority(skb, 0);
+
 	gw_mode = READ_ONCE(bat_priv->gw.mode);
 	if (is_multicast_ether_addr(ethhdr->h_dest)) {
 		/* if gw mode is off, broadcast every packet */
@@ -338,6 +340,9 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 
 send:
 		if (do_bcast && !is_broadcast_ether_addr(ethhdr->h_dest)) {
+			/* WARNING batadv_mcast_forw_mode might add more headers
+			 * in front of the skb. and might even reallocate the skb
+			 */
 			forw_mode = batadv_mcast_forw_mode(bat_priv, skb, vid,
 							   &mcast_is_routable);
 			switch (forw_mode) {
@@ -355,8 +360,6 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 		}
 	}
 
-	batadv_skb_set_priority(skb, 0);
-
 	/* ethernet packet should be broadcasted */
 	if (do_bcast) {
 		primary_if = batadv_primary_if_get_selected(bat_priv);
-- 
2.47.3